300 physical stores setup for the "stack and quick-swipe" parade… I've seen how they manage the big releases. It's pretty efficient. Easily a thousand transactions an hour, if not more than that.
I don't see 5 million being a problem, even if they physically had the stock. But this is a combination of physical locations, online sales, reseller sales, etc. I'm not sure if the 5 million number includes the "pre-orders" we saw previously (2 million in the first 24 hours? And one assumes much more while running up to launch), but I'm going to assume it doesn't...
I think they could have counted a few million more sold if they had the stock. There is a 3-4 week waiting period for ALL models currently. That 3-week gap in itself represents at least a few million units sold but not yet shipped (and so not yet counted as sold by Apple). You can bet if it was Samsung, or Amazon or Motorola, they'd be counting the outstanding "waiting for stock" orders too.
So, yes, perhaps the launch weekend sales of 7 or 8 million DID happen, they're just not counted yet as they couldn't deliver them right away.
Again I wonder about the original pre-orders, and if they're counted into the "launch weekend total". I'd love to know a first weekend number including pre-orders.