Marvel's head of production, Kevin Feige, released a statement that strongly inferred that Norton was being dropped due to an unwillingness to collaborate and share the spotlight. The statement included the following:
Our decision is definitely not one based on monetary factors, but instead rooted in the need for an actor who embodies the creativity and collaborative spirit of our other talented cast members.
Ouch. That is public relations speak for, "We'd like to hire someone who isn't such a dick."
Norton's rep was understandably upset, saying it was an offensive, purposefully misleading, inappropriate attempt to paint our client in a negative light, adding counter to what Kevin implies here, Edward was looking forward to the opportunity to work with Joss and the other actors in the Avengers cast, many of whom are personal friends of his. Feige's statement is unprofessional, disingenuous and clearly defamatory. Mr Norton's talent, tireless work ethic and professional integrity deserve more respect, and so do Marvel's fans.
For his part, Norton responded pretty damn classily. The weird thing is that while what Marvel charges isn't exactly out of character for Norton, neither is Norton's camps that Marvel is unreasonably cheap.
Norton has had a history of somewhat fractious professional relationships. Tony Kaye, the director of American History X, famously has huge clashes with his star, as Kaye hilariously wrote about in an article for the Guardian. Here's a few choice excerpts:
The first screening of my cut had been a success. Then the studio gave me pages and pages of notes, as did Norton...Their first reaction after I bawled them out was to ban me from the cutting room. Eventually they let me in, and I worked with them on re-edits for a year. In that time, I found a whole new film, one that they never allowed me to finish. At one point, they even let Norton work on the editing. I was so staggered by what he was doing to my film, and by the fact that New Line approved, that I punched the wall and broke my hand.
Whenever I argued with Norton, I didn't have a leg to stand on. He could wipe the floor with me because he's a great articulator...Of course, if you actually listened to what Norton was saying, you could hear that none of it made sense in film-making terms: that's not his forte, as you'll know if you saw the movie that he directed, Keeping the Faith. "Pretty fucking awful" hardly covers that one.
Marvel has also had its share of difficulties, most famously falling out with original Iron Man co-star Terrence Howard and replacing him for Iron Man 2 with Don Cheadle, purportedly over salary demands.
So, who knows? Norton has never been the easiest guy to work with. Look at how many times he's worked with anybody twice. That's your biggest indicator in Hollywood if some one's a massive pain in the ass. Still, the usual (well, polite, really) thing to do is to refer to some sort of nebulous "creative differences". What you don't tend to do is come right out and say, "That guy over there? Major asshole!"
But word has just come out that they are in talks with Mark Ruffalo to take over the role. And I think Ruffalo might wind up being a better fit than even Norton. Ruffalo is a bit more off-kilter than Norton; less of a leading-man, more of a character, but still charismatic enough. Could be interesting.