Don't forget the carry on bags - US flyers try to shove the kitchen sink in their carry-on while elsewhere they limit weight (they also are efficient at getting bags out to the carousel, vs AA which can take an hour)
And of course US flyers do this because US airlines charge for checked bags and are unreliable about delivering them, which encourages passengers to carry them on instead. That policy is the airlines shooting themselves in the foot in the chase of (substantial) marginal revenue and selling those who don't check bags on the false claim that the airlines are doing them a favor by saving the cost of bag fees.