As someone who as worked in eCommerce I can say it's not as simple as you lot make it out to be to make major changes to a website.
Firstly you need to bring the site down and host the "Sorry" page.
Then you deploy the new code and make it live internally.
Then you need to run tests and have users check the site is correct and has no mistakes.
If everything is okay then you can make it live, if not then you have to redeploy new code with the new changes and run the tests again. Also you may have to revert the site. Only when everyone has signed off the changes can you make the site live for the general public.
Our major changes happened overnight and could last for hours. I would imagine as the USA is in the early hours of the morning then that is exactly what is happening.
I can guarantee Apple don't even need to do that. They're bound to have another 'internal store' similar to how the higher education one works off IP addresses so they don't have to do that. It should just be a flick of a switch and the new stuff goes live.