True Fox, it is a challenge but that is when the license department contacts the host directly and registers a complaint.
Most good hosts have no problem in taking action against violations once they determine the violation is lagit. It is self serving because they feel if the client is going to violate one license then they have no problem violating any terms (including the hosts).
They will typically contact the client and notify them of the complaint as well as possibly suggest they comply or even warn them of the actions that could be taken. Worst case if the client decides to be a jerk and refuses to do anything to conform, the host under their "we reserve the right" clause can shut the site down. And that always gets their attention.
Hosts dislike clients that cause trouble, i was surprised awhile back because i had the impression (my bad) that russian hosts were horrible or refused to enforce anything, that is what i was led to believe over the years. But one day i found that a russian website had copied and pasted the front page of my old social site on one of their pages and was using it to link to a porn site. I was enraged, so i sent and email to the site and got no answer. Then i sent an email to the host and within 24 hours i received an email that they had contacted the client and that the issue was resolved. I checked and sure enough it was gone. I was happy to see that happen. The point is that many hosts dont want trouble clients.
As i had mentioned there are plans in place to make this better. Such as the possibility of requiring anyone which asks for support to post their site url or have it on their profile. To train those volunteers on here to check first before offering support. It will not happen overnight but it does need to happen and we do need to tighten the noose a bit. Of course we will never catch everyone but it is a step in the right direction and opens the door for new process to be born from the ashes... :)