I think my simplest heuristic for agreeing with your point is how much content there is in the English Wikipedia vs. other languages. I haven't run the numbers, but I'm sure it's also much more US centric (take a look at the # of articles on the US government (current and historical) vs., say, the Brazilian government...)
America just tends to be particularly prolific in producing online content. No, I'm not claiming this as a statistical fact, but I am claiming that's the impression day in an day out so might as well assume as much...
(Dis)claimer: I'm not American