Mant is at the same time for all worlds...authentication servers are all in JP, is what allows us to create characters on those servers, so when they go down all worlds go down.
NA is only a data center, no devs or mant team.

Actually what SE is doing is what any successful international compaly would do, screw the less possible ammount of customers.

Mant times are:

8AM - 6PM +/- hours in Japan, Australia, SE Asia. Office hour are like in the rest of the world from 9am-10am to 5pm-6pm. Mant ends when their prime time starts.
2AM or 3AM - 11AM or 12PM in Europe (Lon, Par, Ber respectively).Thats an off hour, everyone is at their work or school
5PM - 3AM in NA (PDT) prime time for NA

If you think NA has more customers than JP + Aussies + Europe combined, then I want some of what you're smoking

And no...no company does different maints for their servers, Blizzard doesn't do it, NCsoft doesn't do it, Bioware doesn't do it, Nexxon doesn't do it, no way SE is going to do it