Actually tlds may have restrictions and can enforce them. This isn't very common, and most of the past issues with IO has been their very slow time processing registration requests as opposed to content takedowns, but some tlds require ssl and others do restrict adult content. Some restrict things to a given topic (which they get to be the judge of) and others require legal hoops to register such as proving you're a non-profit.

With the explosion of tlds and those tlds being privately owned, there's a good chance we'll see more of these problems in the future though right now it just seems like the owning orgs are just looking for easy money.