Over-simplification of a complex subject.
An analogy would be for a star player who had a good game to claim all the credit after the game and put his team-mates down. Even if the star player did have a great game, all the other members of the team played well and did their part in winning the game -- and helping the star player deliver a great individual performance.
This sort of behaviour (i) is pointless because it relies on speculation about what might have happened had things been different and (ii) displays a real lack of grace, particularly when it is the star player that is doing it.
Many nations (large and small) came together to fight against tyranny during World War II, and their commitment to that cause and their sacrifice was enormous. This is what should be remembered -- not whether one nation's contribution or sacrifice was greater than the others.
"Man, listen to Lance Armstrong claim all the credit for winning 6 Tours de France in a row! You think he'd forgotten there were 8 other guys out there riding for him. What a poor sport! It's just like those guys who bang on and on about the American View of World Ward II"
Note -- this is a stupid example to illustrate the point. Lance is a true sportsman and would never behave this way.