It's not so much I'm annoyed by games and films and so forth when they portray America being invaded by human forces. For me it becomes annoying when the entire Earth is invaded by aliens, and the Americans stand up and say "Yes, we represent everyone on the planet because no one else is worth bothering with."
Which is, I think, why I really appreciated District 9, the original novel 'War of the Worlds' and will probably be thankful for Mass Effect & Modern Warfare 3.
(Obviously MW3 isn't about aliens {that we know of} but it's set at least partially on British soil, so.)