Hey kids, marketing materials!
Disney has released a bunch of character posters for The Avengers, all jammed together in the form of banners. What's interesting is that one banner is all the guys who have had their own movies and the other banner is everybody else. Alternately you could look at one banner as the very heroic characters and the other banner as the villain and the 'darker' (ie black ops, etc) characters. But really it's just that they wanted to get all the name characters on one banner.