There actually has been no official word as to why Maurice Edu's goal was disallowed, but it certainly doesn't look like a foul. Some have speculated that Clint Dempsey was guilty of a foul, Bob Bradley implied that the referee was merely making up the call.
In any event, contrary to popular belief, the referee decision is not the reason why USA failed to pick up the maximum points. And I can say as an American citizen and USA supporter that if the Yanks fail to progress, it won't be because of that call.
USA are in a very favorable position right now, because all that's required is to defeat Algeria.
Besides, I think it's a little too early to start throwing terms like "biggest scandal of FIFA 2010" around. We still haven't seen any game 3's or any knockout matches yet. To date, none of the matches played so far will be as important as the matches yet to be played. If this ultimately ends up being the biggest scandal of the Cup, then I would say that the referees did an excellent job in the knockout phase.