Bungie said them selves, after seeing the amount of money Gears of War raked in and the money the devs got from that, compared to their pockets from Halo, they new they had to make a change. MS was -blam!- them. From the interview I watched I didn't see them say it was originally for 360, so not saying you are wrong just that they had to leave blood sucking MS to make some money for their effort.