To reduce cost this "border router" is probably also running an in-memory cache such as memcached or varnish. So they simply re-created what SuprNova.org did in 2003.
9 years ago this was really novel. SuprNova was the first to introduce a load balancer for both HTML and .torrent hosting.
Aside from that, it doesn't sound like SuprNova's setup was quite as intricate as this. I think that the post above was suggesting that the "caching border router + encrypted VPN" setup was what SuprNova used, but that's not everything that ThePirateBay seems to be using. Also, ThePirateBay only has to host magnet links, which didn't exist (IIRC) back when SuprNova was active. SuprNova had to host all of the .torrent files.
It's simple: the exist node in both Tor and Piratebay has all the legal exposure. That server/caching router/proxy could become impossible to host anywhere. Move it to USA? Expect 1 hour of uptime:-) Russia? Expect 10seconds page load times.
Any experience hosting people out there? Are Sweden and The Netherlands the only few-questions-asked options on town?