NOT.
EBGames only accounts for ~10% of the US video game sales. While they do get a higher percentage of preorder sales, they aren't at 50% of preorders, not even close. And don't say that preorders are actually much higher than 1 million (although, they will continue to grow), as Microsoft would clearly trumpet this all over the place.
Also, at 10% of the industry, which is where they will settle into through the Holidays, let's say that sell twice their preorders, which would be 1 million. That would be 10 million copies of Halo 2 would be sold this year. Not going to happen.
That number is beyond ridiculous.