I remember reading an interview with the developers, and they said they had several offers from publishers when activision dropped the game last year, so if it wasn't Sony, it could of been another company.
On another note, people here keep saying its a good move for Sony, well why should anyone care about that? Its not a good move for a gamer and actually hurts the sales of the game. As great as I think this game is looking, I don't think it's going to get people to rush out and buy a PS3 so what exactly does this time exclusive deal achieve? The 360 and Wii versions are not coming out a good 6 months later, and right in the middle of the Xmas rush of games, hich chances are will hurt sales of it.