I see the logic behind the "it's only a $30 upgrade" complaints. 

 I have an even better solution: why don't US airlines just bump randomly off the flight people who paid the cheapest fare for the economy class, and instead put the ticket on sale for what it would go for last minute travel? It's only a cheap ticket, afterall.

 Even better, this logic could apply to transfer legs of intercity travel: why keep flying people from SFO to NYC with Detroit layover, if their entire trip was worth less than the trip from SFO to Detroit? Why don't just bump them off at Detroit instead (it's a free trip, afterall) and let them book a trip to NYC at market prices?