They consistently target Pirate Bay because of its popularity as a torrent tracker site. The problem is that since they are located in Sweden, the copyright laws are totally different. The MPAA doesn't stand a chance in getting a single cent out of them.

Every time some large company has tried to sue them for money, Pirate Bay has won and walked away without owing a cent.

And yeah, Peter's cocky because they get things like this all the time:
The Pirate Bay - The world's largest BitTorrent tracker

It's not the first time the MPAA has targetted them (unsuccessfully), and certainly won't be the last.