Question: Why was Edward Norton replaced by Mark Ruffalo as Bruce Banner?
Answer: There were disagreements between him and Marvel about the contract. It's said Norton didn't want to be clung to a single character.
Question: How would Bruce be able to get Calcutta? He's made it a habit of never using anything that could be used to track him, so going anywhere, even to another country, would seem impossible.
Answer: People have been smuggled in and out of countries for decades, grease the right palms and talk to certain people, if you don't get in under the radar, phony papers could.
Question: I've noticed a few times in the film they mention "Phase 2." For example, when Fury is talking to the council they bring it up and Fury says "Phase 2 isn't ready." Given that the MCU was broken up into phases, with this being the last film in Phase One (with Iron Man 3 released a year later as the first film in Phase Two), was this an inside joke or nod about the MCU phases, or just coincidence and I'm reading too much into it?
Answer: Phase 2 in the movie refers to the plan executed in Captain America: Winter Soldier, Project Insight which is their next phase for total security of Earth (along with Stark's Ultron program). It is coincidental that it is the same term used for the MCU itself.
Question: On the helicarrier, when everyone is having an argument Steve says to Stark, "I have seen the footage." What footage is he referring to?
Answer: It could be carefully selected bits of Tony at his worst moments, like when he was a hard drinking irresponsible party animal.
Question: Why does Captain America say that Fury has the same blood on his hands that Loki does? It seems unlikely that he is being literal to the point that the fact that Fury touched Coulson's dying body means that he has the same blood on his hands as Loki...What am I missing?
Chosen answer: It means Fury is just as guilty for Coulson's death as Loki is.
How?
Question: How did Loki know that it was Natasha who brought Bruce onto the Helicarrier?
Answer: He doesn't mean her, he means them, the Avengers, they have brought the Hulk on board.
When Natasha calls Loki a monster, he responds, "No, love, you brought the monster."
And with the "you" he refers to the Avengers, not her specifically.
Actually, it was Natasha who brought Bruce. She had been informed by Coulson that she was specifically requested to bring Bruce with her so Loki's comment "You brought the monster" was accurate.
Answer: In addition to lionhead's answer, there are also rumors that Norton wanted more creative control over the character and franchise, as evidenced by the fact he did frequent uncredited rewrites on the set of "The Incredible Hulk" and also even ghost-directed a few scenes while director Louis Letterier was tied up with other obligations. Given the complexity of the MCU, the producers and studio didn't necessarily want cast-members to exercise more creative control over the films early on because it could undermine their long-term plans.
TedStixon