With games like Gears of War and Halo, your large name, sequel titles. You will sell them at Christmas regardless. So just release them whenever. You don't have to worry about attaching some games to consoles.
If the game is good enough and lasts long enough, people will still buy it for Christmas 6 months later if they haven't already got it. If its a mediocre game, it will probably won't get noticed. At the same time people will probably only buy 1-2 games for Christmas and it will likely get destroyed by a better game. Kind of like how orange box destroyed all other shooters trying to release beside it.
Now maybe in another 5 years they'll catch onto pricing. Valve seems to have already got the idea and is moving ridiculous amounts of product with their sales.