We've touched on this recently, but if you need a pointer as to how important "pre-sales" on the PC are becoming, you should check out Aion's "sales figures".
The upcoming MMO has already "sold" 400,000 copies. Those aren't $US5 pre-orders, those are people stumping up the entire cost of the game in advance. A game that's not even out until next week.
If you ever needed proof that betas are becoming less about QA and more about marketing, please see the above figure.
Aion preorders near 400,000 [GameSpot]