Frontier offers extra legroom in coach for a small fee. My wife and I often chose that option before we switched to Southwest Airlines.
You're not going to believe this if you read my comments, but I'm questioning what role the FAA has in deciding seat size. The FAA's role is to make sure planes don't bump into each other, that planes can actually fly, that two planes don't try to occupy the same runway space at the same time, etc.
Is the NHTSA now going to decide whether seats in automobiles are cushy enough?