I don't think employers allow less vacation time because most Americans can afford air travel; I think employers are simply stingy and do not want to pay for benefits overall.

I tend to look at more than clear-cut cause and effect. I agree that rapid travel is not "the reason" Americans have less vacation time, but these are part of the overall pattern. Like the role of the automobile in the suburbanization of American cities. I would say that rapid travel was one of many factors that made it easier for employers to reduce vacation time.

I do agree, though, that rising costs of rapid air travel will not result in more vacation time for Americans. It could be that the age of globetrotting is simply over.