They're coordinating a major change to, probably, a quarter of their product line across a dozen localised websites in multiple timezones and countries. That's a bit more tricky than Amazon changing the price of an economy pack of incontinence pants in Germany (on a platform that is designed to support a vast catalog of products from multiple vendors).
Apple are actually pretty unusual in that their new products are typically available to order in multiple countries immediately after launch. That will come with its share of logistical problems.
#engagebrainbeforetweeting
Not true AT all!
This is the entire point of CMS systems. You update in one place and the changes are automatically filtered down with localized language options. This isn't so complex that it requires the store to go offline for an entire day. Not only that but most CMS systems have a timed post function so they can update their product pages whenever they want and just set the timer to automatically post at the appropriate time. Or the content exec just presses a button as soon as the presentation ends.
I would bet you a million dollars these new product pages were created weeks and approved ago and are waiting for someone to press a button at the end of the presentation - they wouldn't risk doing it the day off when something could go wrong or the copy would be wrong. This is done purely for marketing reasons.
The only acceptable reason is simply because they just don't want to sell stuff that's "outdated" so it's done to "halt" the sale until the new stuff is announced. But it isn't like they close their retail stores to prevent people from buying "old stuff."