Originally Posted by DrCosmic
Because 1) It establishes that the favorite hero on the squad is not capable of handling the new threat level on his own, validating the entire movie. 2) It establishes Hulk as 'the strongest there is' so that he can properly serve his purpose as the plot hammer. 3) It gives Tony a chance to have his 'I can't do it on my own' arc within the film, since he's the only one, other than Hulk, who's used to running solo.
Yeah, Tony is going to come with the team spirit of the entire Avengers, and not only order Hulk around, but use what he's learned in his character arc to whomp on whatever Loki throws out... as opposed to just showing up to win every battle and make us wonder why bother having the Avengers if Iron Man can handle it all.
I don't think the plot will end up being like this.