I just don't think that the concept of Hulk connects with the general audience in all honesty. Even if you change certain aspects of him to bring him more in line with the comic (eg make Hulk the star, make him talk, make him intelligent etc) the fact is that the general audience still see a big green monster and think that it is a mindless movie. Lots of people (friends, colleagues etc) I know just groan when they hear about a Hulk movie, whichever incarnation it was (2003 or 2008). Even when the Hulk TV series was showing, my mom would groan at the idea of it, but would more actively watch the live action Spider-Man with me, even though she wasn't exactly a comic fan. It didn't matter that Bill Bixby (the human form of Hulk) was the star - the fact that there was a raging brute of a monster just was off putting.
Friends of mine (non comic fans) even prefer Iron Man to Spider-Man. Hulk just doesn't seem like all that much of a viable concept to general audiences. He might be A-list in the comics, but I don't think he is in the movie world. Heck, Hulk himself might even be a reason general audiences might not want to see the Avengers. If they do, it will be because the excitement of watching Robert Downey Jr as Tony Stark will override the disdain of watching the Hulk. They shouldn't push Hulk as too much of a main character compared to the big three.