I think its prospective sales are being vastly overestimated, and I have no idea where you're getting your numbers from. Gears of War sold 5.2 million on the 360, which is pretty far from the 6 million you're denoting. Halo: Combat Evolved sold about 6.4 million, which is nowhere near 8 million. And Halo 2 is close enough to your estimation so I won't really bother.
Gears of War 2 will be big, but the 360's hardware numbers haven't made large enough gains to boost a sequel's sales numbers by several million.







