A .torrent file merely contains some file hashes, tracker address(es) and other misc data,
none of which is copyrightable. A tracker merely helps users connect to other users;
no copyrightable data is ever stored on it or passes through it.
That being said, those defenses are more on the technical side. On the literal side, it's obvious that a TBP torrent for Iron Man aXXo rip.avi is for copyrighted content. It's on this basis that they go after trackers. By helping people to find the torrents they want that
relate/refer to (but don't contain themselves) copyrighted content, i.e. making categories like Movies / Music / Anime etc, it's possible to get some trackers on the charge of "assisted" copyright infringement. That's what got mininova took down, as well as torrentspy.
By merely indexing torrents and not hosting them yourself (google can do this, the **AA aren't going to go after google), and using a completely anonymous tracker system like
OpenBitTorrent (read that page), it's alot harder to take a system down.
The original owners aren't allowed anywhere near TBP anymore, but they have other people who can manage the site. The court case was against the 3 owners, not against the site itself. Others are free to administrate it on their behalf.