Another example with regard to others regarding simultaneous game releases.
According to VGChartz data the 360 has an install base advantage of about 10% here (which is IMO already a great result considering a 17 month headstart for the 360 and higher entry pricing for the PS3).
Although others data are probably the hardest to track here on VGChartz, the data suggest:
Godfather II sold better on the PS3, despite the 360 should have sold better taking into account install base.
The same goes for other recent releases like Resident Evil 5, Street Fighter IV, the Wheelman, Tom Clancy’s HAWX, Fifa 09, etc.
The only recent multi-platform game I could find which sold slightly better on the 360 as should be expected is Call of Duty: World at War.
So this trend seems to be valid worldwide.