Well that may be true, but if M$ were to release a 720 at Christmas, do you really think that they would launch Halo 4 on the 360? They plan these things years in advance, and they would not be that stupid.
I agree that a big launch doesn't necessarily mean that the new console won't be out then, but it is very important to have games coming for the new console, and something like Halo would move consoles. GoW less so, which is why it is probably more important to use it to continue shifting PS3's rather than push it back 6 months on to a PS4







