In an interview with IGN Japan (and reported in English by IGN), Crystal Dynamics studio head Scot Amos explained a little about how and why that exclusivity deal came about, citing the relationship between Marvel and Sony (which spans both the game and film industries).
However, if you are worried about more characters being restricted to specific systems, it doesn’t seem like that’s happening. “That is the only character that we are doing that way,” Amos told IGN Japan. All of the other post-launch heroes (like Hawkeye) will be available to people who own the game on any platform – and for free.
Marvel’s Avengers releases on September 4 for PS4, Xbox One, and PC, with next-gen versions to come later. For more about the game, read our hands-on impressions from the beta.