Its ridiculous to say that Halo 3 will not move consoles. Unless the game is completely broken, it will sell consoles. It may suck, and marketing alone will move a ton of consoles.
It will for sure move consoles, I don't think that is in any doubt what so ever. The question though is how many. Most likely it will not reproduce the success of Halo 2 at the current price point. But maybe MS is going for the two tops strategy Kim Shane talked about in an interview quite some time ago. 1st sales top at launch and the 2nd one at christmas as the title is still quite "fresh" and might be aided at that point also by a price drop...