Hmm possibly but doubtful. Of course it'll move some hardware but not too many games actually move hardware outside of Japan. What moves hardware in America when a big game releases? Increased shipment and advertising. And it's obvious Fable 2 will have brought this but it's a core franchises that doesn't stretch to far out into the mainstream. I mean it gets mainstream buys of course but it's not like your Gears of War or Halo equivalent when it comes to the mainstream.
I do agree with the diminishing returns when it comes to exclusives as well. So it'll move some hardware... possibly and extra 25k-50k but it's not going to be a huge mover. Nothing where we'll be screaming and yelling next week about its awesomeness to move hardware.