I disagree, because Crackdown had a beta for Halo 3 and didn't sell in the range of what you are expecting here. So if we are treating Halo ODST as a spinoff title that isn't expected to get the same sales as Halo 3 I don't see why it would sell like you are predicting because of a demo when Crackdown didn't
http://vgchartz.com/games/game.php?id=405®ion=All
...









