We can't tell.
What would've happened if the game was released last holiday season, had more hype (due to being exclusive), was a better game (as almost all exclusives are)?
How many of the pepole who bought it for the 360 also have a PS3 (and would've bought it for the PS3 if it was exclusive), how many pepole who only own a 360 would've bought a PS3 for XIII if it was exclusive?
We don't know.
So the game probably sold more on both HD consoles combined than on what it would've sold on the PS3 alone, but, with all that i've said earlier, we can't tell for sure if those extra pepole were worth the price of porting the game for the 360.
Bet with Dr.A.Peter.Nintendo that Super Mario Galaxy 2 won't sell 15 million copies up to six months after it's release, the winner will get Avatar control for a week and signature control for a month.
