Well one thing to remember is that a pre-order is not a sale. Can't say how many times I've pre-ordered a game and ended up not buying it, either switching my pre-order to something else or canceling it all-together.

Not to mention it's not a sale till it's paid for and picked up anyway, and also if you go that route you have to go with the pre-orders of Lich King which should probably amount to 3 - 4 million I'd hazard a guess. :)

Not saying WoW is god, sure I play it and have a pre-order if for WAR myself, just pointing that out.