To sue someone it requires
-Hiring lawyers
-Going to court (spending the time there + lawyer costs)
-Suing someone who can actually PAY the fine
So yes... there is NO reason for tq to sue private servers.
As for the law... Redistributing copyright files is illegal. So if you are not using hacked tq server files (custom source, not binaries) and you aren't using any images of theirs on your website and aren't distributing their client then it's fully legal.
The ONLY thing commonly illegal about non bin servers is distributing the client but you can easily get around that (don't host the client yourself, use current patch so that they can use the official client, etc)