user315: The U.S. Chess Federation piloted a 175-move draw rule in the fourth edition of its Official Rules.  This interesting rule ended a game automatically after 175 moves, whether or not either player had claimed a draw.  (The rule also included some verbiage regarding a particular kind of chess clock, but it is not clocks that I ask about today.)
In the fifth edition of its Official Rules, the U.S. Chess Federation abandoned the 175-move rule.
I liked the 175-move rule and was sorry to see it go, since it lightened certain burdens of subjective judgment and of overextended hospitality from the shoulders of a tournament organizer.  I suppose that someone else must have disliked the rule or it would not have been abandoned, but at any rate, is there an interesting story behind the abandonment of the rule?
There was this (PDF) at the time, but it did not explain much.
UPDATE AND APPENDIX
@AndrewNg has given an interesting, informative answer; but an answer to a slightly different question than the question I had meant to ask.  At the risk of so long an update that few may read it, let me clarify.
Insofar as I have correctly inferred its purpose, a hard limit on the number of moves in a game exists to protect the interests less of the players than of the players' host (the tournament organizer, hall owner, etc.), without stranding the host in the unfair, distasteful position of having to interject a subjective, third-party judgment into the game.  Examples of potentially relevant games include Nicolic v. Arsovic, Belgrade, 1989.
Of course, it is possible that I have misunderstood the rule's purpose.  The reason for my understanding however lies in the crucial difference between the 50- and 175-move rules:  the 50-move rule takes effect only when one of the players chooses to invoke it (which the aforementioned Nicolic and Arsovic declined to do); whereas the 175-move rule automatically takes effect, without consulting anyone's subjective opinion in the matter.
In short, the 175-move rule prevents the unlikely but nevertheless mechanically regular (and possibly indeed sportsmanlike) play of the game of chess from forcing a mechanical irregularity when the host's patience runs out.
Another, related purpose of the rule -- a purpose explicitly mentioned in the fourth-edition rulebook -- was to relieve a tournament director of the burden of adjudging "insufficient losing chances" in certain technical circumstances.
I admit that, like @AndrewNg, I too doubt that it was ever the rule's purpose to guarantee that every, theoretically forced mate could be carried to its infinite conclusion.  Indeed, like the 50-move rule, a 175-move rule if enforced becomes a new, mechanical constraint on the theory of the game; such that -- per theory under the rule -- 176-move mates simply no longer exist.
Maybe the new mechanical constraint on the theory is precisely what the fifth-edition rules committee did not like, but I cannot substantiate such a guess.  Thus the question.

user4418: 
I liked the 175-move rule and was sorry to see it go, since it
lightened certain burdens of subjective judgment and of overextended
hospitality from the shoulders of a tournament organizer.

You will be pleased to know that FIDE also liked the idea so much that they have implemented a 75-move rule which took effect on July 1 2014

user1382: EDIT: As I reconsider the question, I believe that adjournments played a role in the abandonment of this rule, as detailed in my comment below. I understand that this still is not an exact answer to the question and I suppose only the USCF committee would have the answer to that :)
Also, there is the problem of neither player invoking the fifty-move rule, as referenced in your appendix. However, I have never encountered such a scenario in my chess-playing career, although I'm sure it has happened. I suppose such an occasion is extremely rare and the organizer probably would step in.

I cannot supply the story given by the USCF on the subject as I couldn't find any specific information online. I can, however, supply my reasoning on why such a rule would be taken out.
In modern chess, there no longer exists (practically) the need to claim a draw. As a result of delay clocks, the fifty-move and threefold repetition rules take precedence. Therefore, there are no real "judgement" calls to be made as the TD doesn't have to make any decisions regarding draw claims - he simply has to count the number of moves before the last capture/pawn move or see if the resulting position from the claim occurred at least three times.
Therefore, if a game were to progress past 175 moves, there must have been captures or pawn moves within the last fifty. This implies that there is a fair chance that one player can emerge victorious. Even if the game is a technical draw, it is ensured that the game will not progress fifty moves past the last capture or pawn move. 
It is for the aforementioned reasons that FIDE re-established the strict fifty-move rule in 1992 even after many winnable positions were proven to take more than fifty moves (without a capture or pawn move) as referenced by Akavall in the comments. Indeed, before this date FIDE had changed the rule to allow certain exceptions, but the number of these winning positions grew so large that it was easier to leave a strict limit in place. This likely influenced the abolishment of the 175 move rule as there were no more exceptions to be had of the fifty-move rule.

315: <p>The U.S. Chess Federation piloted a 175-move draw rule in the fourth edition of its Official Rules.  This interesting rule ended a game automatically after 175 moves, whether or not either player had claimed a draw.  (The rule also included some verbiage regarding a particular kind of chess clock, but it is not clocks that I ask about today.)</p>

<p>In the fifth edition of its Official Rules, the U.S. Chess Federation abandoned the 175-move rule.</p>

<p>I liked the 175-move rule and was sorry to see it go, since it lightened certain burdens of subjective judgment and of overextended hospitality from the shoulders of a tournament organizer.  I suppose that someone else must have <em>disliked</em> the rule or it would not have been abandoned, but at any rate, is there an interesting story behind the abandonment of the rule?</p>

<p>There was <a href="http://archive.uschess.org/docs/pdf/43-56CommitteeRep02.pdf" rel="noreferrer">this (PDF)</a> at the time, but it did not explain much.</p>

<p><strong>UPDATE AND APPENDIX</strong></p>

<p>@AndrewNg has given an interesting, informative answer; but an answer to a slightly different question than the question I had meant to ask.  At the risk of so long an update that few may read it, let me clarify.</p>

<p>Insofar as I have correctly inferred its purpose, a hard limit on the number of moves in a game exists to protect the interests less of the players than of the players' host (the tournament organizer, hall owner, etc.), without stranding the host in the unfair, distasteful position of having to interject a subjective, third-party judgment into the game.  Examples of potentially relevant games include <a href="http://www.chessgames.com/perl/chessgame?gid=1268705" rel="noreferrer">Nicolic v. Arsovic, Belgrade, 1989.</a></p>

<p>Of course, it is possible that I have misunderstood the rule's purpose.  The reason for my understanding however lies in the crucial difference between the 50- and 175-move rules:  the 50-move rule takes effect only when one of the players chooses to invoke it (which the aforementioned Nicolic and Arsovic declined to do); whereas the 175-move rule automatically takes effect, without consulting anyone's subjective opinion in the matter.</p>

<p>In short, the 175-move rule prevents the unlikely but nevertheless mechanically <em>regular</em> (and possibly indeed sportsmanlike) play of the game of chess from forcing a mechanical <em>irregularity</em> when the host's patience runs out.</p>

<p>Another, related purpose of the rule -- a purpose explicitly mentioned in the fourth-edition rulebook -- was to relieve a tournament director of the burden of adjudging "insufficient losing chances" in certain technical circumstances.</p>

<p>I admit that, like @AndrewNg, I too doubt that it was ever the rule's purpose to guarantee that every, theoretically forced mate could be carried to its infinite conclusion.  Indeed, like the 50-move rule, a 175-move rule if enforced becomes a new, mechanical constraint on the theory of the game; such that -- per theory under the rule -- 176-move mates simply no longer exist.</p>

<p>Maybe the new mechanical constraint on the theory is precisely what the fifth-edition rules committee did not like, but I cannot substantiate such a guess.  Thus the question.</p>
 4418: <blockquote>
<p>I liked the 175-move rule and was sorry to see it go, since it
lightened certain burdens of subjective judgment and of overextended
hospitality from the shoulders of a tournament organizer.</p>
</blockquote>
<p>You will be pleased to know that FIDE also liked the idea so much that they have implemented a 75-move rule which took effect on July 1 2014</p>
 1382: <p><strong>EDIT:</strong> As I reconsider the question, I believe that adjournments played a role in the abandonment of this rule, as detailed in my comment below. I understand that this still is not an exact answer to the question and I suppose only the USCF committee would have the answer to that :)</p>

<p>Also, there is the problem of neither player invoking the fifty-move rule, as referenced in your appendix. However, I have never encountered such a scenario in my chess-playing career, although I'm sure it has happened. I suppose such an occasion is extremely rare and the organizer probably would step in.</p>

<hr>

<p>I cannot supply the story given by the USCF on the subject as I couldn't find any specific information online. I can, however, supply my reasoning on why such a rule would be taken out.</p>

<p>In modern chess, there no longer exists (practically) the need to claim a draw. As a result of delay clocks, the <a href="http://en.wikipedia.org/wiki/Fifty-move_rule" rel="noreferrer">fifty-move</a> and <a href="http://en.wikipedia.org/wiki/Threefold_repetition" rel="noreferrer">threefold repetitio</a>n rules take precedence. Therefore, there are no real "judgement" calls to be made as the TD doesn't have to make any decisions regarding draw claims - he simply has to count the number of moves before the last capture/pawn move or see if the resulting position from the claim occurred at least three times.</p>

<p>Therefore, if a game were to progress past 175 moves, there must have been captures or pawn moves within the last fifty. This implies that there is a fair chance that one player can emerge victorious. Even if the game is a technical draw, it is ensured that the game will not progress fifty moves past the last capture or pawn move. </p>

<p>It is for the aforementioned reasons that FIDE re-established the strict fifty-move rule in 1992 even after many winnable positions were proven to take more than fifty moves (without a capture or pawn move) as referenced by Akavall in the comments. Indeed, before this date FIDE had changed the rule to allow certain exceptions, but the number of these winning positions grew so large that it was easier to leave a strict limit in place. This likely influenced the abolishment of the 175 move rule as there were no more exceptions to be had of the fifty-move rule.</p>
