I just thought about something...
Say these orders are mistakes. Regardless of that, I think BestBuy is going to have to pay fees to the credit card companies for the use of all these cards.
Generally, these fees are 1~3% of the transaction price. Assuming it was 2%, that would mean that they would likely pay around $130,000 for nothing if there really were around 10,000 orders.
So, it's already going to cost them that. Then there are the man-hours that they've spent with customer service. Then they're going to have to make the effort to cancel these orders, email everyone, and do damage control. On the side, you have people mumbling about lawsuits (And despite the fact that they wouldn't get very far, it would be an annoyance to BestBuy).
All in all, they don't have much to gain by cancelling all these orders. If the pre-orders were expected but the system was used a little early, it's most likely that they'd simply honor the orders. If the pre-orders were unexpected, they're going to analyze whether or not it would cost more to re-allocate the systems or to cancel the orders.