My wife and I travel together a great deal, almost always in FC. Occasionally we are assigned separate seats and generally there is no trouble getting someone to change. However, neither one of us thinks that anyone is under an obligation to change for us, especially when the seats are quite different, and if nobody will, so be it. Everyone has his favorite seat and who are we to try to obligate someone to please us by displeasing himself. Although, you do know that the guy who won't change from 2B to 3B is usually just being a jerk.