Not just that. I'm pretty sure i read somewhere that they employ a very decentralized and redundant architecture, where almost nobody is in a position to compromise the entire setup. They had to evolve this way after it became clear that Swedish authorities were after them. From what I understand, even their own admins often don't know where their servers are anymore.
This resistance to physical attacks is why countries eventually started blocking it at the consumer end, through ISP-enforced bans.
It's a shame they can't talk more openly about it, I'm sure they could teach some valuable lessons in reliability.
So, the Pirate Bay's servers are in countries that either don't care to enforce or aren't able to enforce copyright law.