To be fair, it does matter. The 360 has moved a tremendous amount of software this gen and has a stellar attach rate and there's no doubt that it is the clear 3rd party winner so far because of it. I think the one year head start did more than most think.
As for Call of Duty; I honestly don't care one way or the other since I feel that the series has gone stale quite some time ago (since Modern Warfare) but I just wonder how it will compare to Modern Warfare 2 commercially.