6 months is kinda weak, MS should have locked these up for twoish years.
Though honestly I think in the long run we are only going to see more and more first party exclusives and everything go multiplatform.
The lists have been shrinking every gen
http://en.wikipedia.org/wiki/List_of_video_game_exclusives_(seventh_generation)
This list is missing some games like console exclusive Splinter Cell Conviction, etc.
It's just that simple.