Trivia: The photo of Cap in Tony's tower has the number #25 - the issue number of the comics in which Captain America dies.
Trivia: When Thor and Hulk battle on the helicarrier, Thor hits Hulk, who collides with a Harrier jump jet. The prop Harrier which Hulk hits is the very same one that Arnold Schwarzenegger flew in True Lies.
Trivia: The first movie to ever gross over $200 million domestically in its opening weekend. (And somewhat coincidentally, it was released almost exactly ten years to the day after "Spider-Man" - the first movie to gross over $100 million in its opening weekend, and also based on a Marvel property).
Answer: During the end sequence of The Incredible Hulk Banner discovers that he can aim the Hulk in the right direction, give it a goal, which he uses to defeat the Abomination in that film. Key to that appears to be willingly accepting the transformation into the Hulk, which he does by choosing to jump from the helicopter. On the Helicarrier, Banner doesn't want to transform, it's caught him by surprise, he's fighting it, which is why it takes ages, is seemingly very painful and, as an involuntary change, the Hulk is out of control. In the final battle, Banner chooses to make the transformation, to "suit up", as it were, and thus the change is swift, painless and results in the cooperative Hulk capable of working with the others towards a goal.
Tailkinker ★