I would instead suggest that since Apple is in control of their supply chain process, then they more likely kept a certain number of devices aside in just such an instance. After all, how else do certain VIP consumers get these devices ahead of others (a la Sports Illustrated and ESPN)?Apple has made a lot more 7's and 7 Pluses available for reservation for those who went through the Apple Upgrade Program. Doubt they manufactured so many so fast so they must have taken inventory from carriers. Perhaps AT&T got hit the hardest.
While I think you're right that the manufacturing aspect hasn't been sped up, I think it also pays to remember that Apple's been at the manufacturing business of devices and computers for decades, and they could be reasonably expected to hold back a certain amount of inventory for such situations.
I know I'm going on about this, but I'm trying to insert business-related rationality into the discussion.