We can only pre-order something or continue to pre-order something if we can absolutely guarantee the unit allotment come launch day. That's a customer service issue.
The online site usually will take CEs, including ones we cannot on a store level, because anything sold there is a fraction of what moves in stores. They don't really have to worry about unit allotments.
In terms of WarCraft, I think the company probably did hit some kind of number that Activision Blizzard gave them for initial shipment. I can say that I racked up a dozen or so pre-orders on the day the SKU was activated in the middle of a work week. That's pretty crazy. I imagine high volume stores, PC-centric stores and tourist locations did unprecedented business in terms of reservations.
Usually in these situations, a GameStop buyer will go back to the vendor to negotiate more units based on the reservations and something works out. Usually.
This is Blizzard, so who knows. I'm sure they wouldn't try and create an artificial shortage, because they want to push as many units of an expansion at full price out the door as soon as possible. Especially since the marketplace has seen a viable alternative pop up in recent days.
