I have a theory...and it's really only that, but it makes sense to me...I think they're building up on hand stock for Apple stores so that on release day, more people are going into the store and walking out happy, considering how important it is to the stores to have customers leaving completely happy and satisfied (which is why they'll bend over backwards at times to satisfy requests from customers who bring their products in for service, sometimes WELL out of warranty).
I almost think the pre-order is always a "testing the water" scenario, and now they see it's going to be an absolute swarm this weekend, and I think we'll see some insane sales number after Sunday is over.