They have a North American branch, FYI.
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Because if the two data-centers aren't synched correctly, that is, use the exact same configurations, then login issues akin to the error 90000 into an unresolvable 3102 due to your character being lost in limbo can happen. That's because despite the game-world servers being separate there is only one login server (Because that enables NA players to play in JP servers).
So yes, they need to enter maitenance mode at the same time.
The North American branch has nothing to do with the game FYI. So the Devs which are all in Japan will be doing it on their time, not your time. This will be how all maintenance will be handled, if you don't the door is right there and don't let the door hit you on the way out.
Why not put it this way. Say you're working at international corporation, would you stay at work until near midnight to do a job when you could just as easily do it in your daytime hours just so your international customers can access your product for that one day, whilst annoying the customers who could more easily come to your physical location to complain?
Thank you for doing your best, glad to see they are telling us stuff. Keep it up.
Me and the rest of Asian and oceanic players always got our maintenance on our prime time in WoW. We sucked it up cos we knew its an American based company. Square is a Japanese based company, maybe its time our NA friends learn to do the same ^_^