Cinema Blend posted a piece on John Favreau's relationship with Marvel Studios, and if true, it doesn't look like terms are that friendly at the moment. According to the piece Favreau negotiated a higher salary for Iron Man 2, and Marvel can't afford him for a film as big as The Avengers, given the big names and special effects budget. And apparently Iron Man 2 isn't the film he was trying to make. It sounds like there might have been so much Marvel interference, most of it to do with shoehorning Avengers elements into the movie, that both Favreau and Robert Downey Jr. were disappointed in the final product. The source of all this in the article is anonymous, so... you know: grain of salt. It's suggested that a big part of the reason Joss Whedon got the job on Avengers is he's cheap. He's a name we all know, but he's only directed one feature.