Every Tuesday night (for me in Australia) Blizzard goes down for maintenance or some bullshit. From what I can remember this used to be because of WoW and maintaining all the servers or whatever.

But now with Battlenet ap, all games are integrated into it (Hearthstone, Diablo, Starcraft, HOTS and WoW). And the entire thing goes down every Tues night for several hours!! WHY?!?

As far as I know - no other games company has this weekly downtime. Does anyone know why from a tech perspective, or have any ideas?

Blizzard's servers aren't mirrored. They're a bunch of lazy dumbfucks. So they're stuck taking them all down in order to apply security patches, hardware upgrades, stability testing, etc.

EVE Online has a daily downtime to do server maintenance, though it usually lasts for less than twenty minutes. These also happen to be in the middle of aussie prime time, which sort of makes sense as there's only one server and this is when there's the least people online.

Having mirrored servers is expensive as fck though, right??

It's a little more than double as expensive as one server (redunant hardware and a little work to set it up)
Server farms for an online game should be pretty expensive though. I'd estimate low 6 digit figures.

lol as if they don't have the money for mirrored servers.

That definitely seems to be the common misconception. I used to think that way as well, but then I started to wonder how all the other games' development is paid for since they theoretically rely on box sales. And then what pays for the enormous staff supporting all of their games. I'm sure they're making a ton from WoW (though probably not as much as they once were), but WoW is probably funding all of Blizzard.

They might not have a build engineering team experienced with seamless server migration (which is not a trivial task for products with constant activity: you have to handle migrating users on the old servers with the new database, for example), and don't want to invest in something that likely isn't costing them money right now and wouldn't be saving them money in the future. Though this would be surprising, considering WoW.

Or they silo their hardware spending by game, meaning the moneymaker (WoW) is going to get new servers before any other game. Likewise, their build engineers could all be allocated to WoW, and the architecture for downtime-free data migration is not in place and will not be prioritized for SC2 or other individual games. Combining server maintenance is also easier than maintaining them all separately, and in software engineering, 'easier' means 'cheaper.'

I'm more surprised that they're doing weekly updates for their servers. What are they constantly changing with such urgency that cannot be accomplished via patching?