Consider that Modern Warfare 2 is at 1,022.92, http://www.simexchange.com/stock.php?id=556, and that it was not an exclusive as Halo: Reach is. Halo is a franchise with much more hype historically than CoD. An estimate I saw read that Halo 3 sold more than 12 million copies. Many more gamers have purchased 360's since Halo 3's release and Halo will probably remain the multiplayer game of choice for at least the newer, casual gamers. Unless I'm missing something, I don't see any way Reach sells less than 13-14 million copies and I think the pre-release hype will push this stock higher than that. I think the more than 1 million gamers signing up for the beta on the first day alone, http://xboxlive.ign.com/articles/108/1089044p1.html, speaks significantly as to how this game will do.
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There is no way it will sell 11million.
That's 1 in 6 or 7 attach rate for lifetime of the 360. Not gonna happen.