As I've mentioned elsewhere:
The Avengers are, on paper, a special unit of S.H.E.I.L.D. Before you ask, no, it's not making 616 more like the ultimate line. It's just the U.N.'s way of keeping track of them, which, logically, the U.N. would do. They're basically doing the same things they were doing before, but now they get all sorts of cool toys from S.H.E.I.L.D., and Cap has to file reports to Nick Fury. Speaking of which.....
Because the Avengers are now a much more international group, they've had a roster change that shows this. The current roster is:
Captain America
Red Gaurdian II
Herculese
Sabra
Caprain Britain
Iron Man
Shaman
Collective Man
Namor
Black Panther
Thor
and, suprise of suprises, Dr. Doom. Now, I bet your asking yourself, "why the **** is Doom on the Avengers?" Well, Latveria has become a major export of technological goods by now. If you own something electronic, it's either from Japan, Wakanda, or Latveria. The nations of the world don't want to piss Doom off. So when he says he wants to join, they sort of force the team to let him. Now, why does he want to join? Well, as always, he has his own agenda. He's playing the team. The team knows this. But they really can't do jack**** about it. Over the course of the series, what he wants from them becomes more obviouse. And it ain't pretty.