^^I'm with Andrew.
The Xbox fanbase for Halo is insane, it's a cultural phenomenon that is on ONE console, not multiplatform.
However, Gears has sure made a name for itself, so I guess it could happen. It only has 18 months of clout behind it though, and the graphical updates are only spotty (it's better overall but it's nowhere NEAR the graphical update from H1 to H2 or H2 to H3).... 3 years between equals will surely produce better graphical results than 2 years (GoW).
I am so stoked for GoW2 though... especially that they are fixing the probs that GoW1 was PLAGUED with!
Halo3 sales: 8.1 million
(SOURCE)
GoW sales: 4.5 million
(SOURCE)
^^ The numbers don't lie.