Money? To some extent.
I think it's more to do with the original XBox and the fact that it could have just as easily been called "Halo Machine." That's what made the XBox cool, and that cool factor carried the XBox 360 with it's early launch. That 1 year advantage was the best move they ever made, capitalizing on the growing poplarity of the XBox (even if you didn't own one, it was very likely you played one) before competitors hit the shelves.







