This unnecessory vista exclusiveness sucks , if the game can run on a 360 it can work on XP too. If the game was using exclusive dx10 features and could not be possible on the dx9 generation of cards it would never come on a 360. Alan wake would be on xp if they wanted to . I ran games on vista RC1 and they ran like sh*it. Although this does not represent the experience on the full version of vista with proper nvidia vista drivers(as in my case) but the current picture is thumbs down. Crysis is not a vista exclusive , the vista version will enjoy the perks of Dx10 but they have not forgot the huge number of xp gamers who r not in position to switch over vista as it comes out. According to crytek 'if you have Windows Vista and an older DirectX 9 card, you should still see better performance with Windows Vista than Windows XP, even if the hardware remains unchanged'. Sounds good but its yet to be seen.
The game companies(other than MS game studios) will be fool to produce vista exclusives so early , the adaptation of the new os by users will take time.