It still baffles me they have to take down the whole website this early to prepare for an update. Maybe it is still for marketing hype but would think they would be beyond that now.
I really, really wouldn't want to second-guess the logistics of these launches beyond suggesting that phrases like "horrendous", "nightmare", "can of worms" and "rather them than me" are probably understatements.
.remember, they're co-ordinating a launch
internationally across multiple time zones both online
and in bricks-and-mortar stores (even if only the "capital" stores have stock or demo hardware, they all have to be ready to display posters, answer questions and take orders - but with Apple's obsessive secrecy, I bet a lot of staff will only discover the details half an hour before we do). They also have to have a "line in the sand" for accepting orders for the outgoing model, when the announcement could happen before, during or after trading hours where the customer lives.
Usually, a company will have a big "trade only" launch in their home country long before the product actually turns up on shelves and the consumer advertising campaign kicks off, and often
months before the international roll out. Apple launch
simultaneously for at least the major international markets on day one - often with the product available
immediately or, at least, they announce a firm date for orders within a few weeks. I can't think of any other example of product launches comparable in scale, speed or public profile to these Apple events.
...and just imagine the gnashing and wailing of teeth if someone fat-fingered the currency conversion and the new Watch was listed at the equivalent "$39.99 on the one of the international website for 30 minutes: Mom & Pop's cookies could get away with it, but Apple would be dealing with a million orders from entitled morons around the world who'd seen the tweet and ordered one via a web proxy.
Edit: that should be "wailing and gnashing of teeth" of course, but hey, it's an internet post - don't expect me to cross every "i" and dot every "t"...