Is it trademark, or IP. If someone made a list of Mickey Mouse jokes, Disney's law department will send them a letter too. Chuck Norris is a person/name but also a persona.
Also, perhaps it was Norris' lawyer acting on behalf of him. Maybe he didn't even know about it.
It's not quite as cut and dry as you suggest. Besides, in which way was a trademark being violated? Last I knew merely talking about and referencing a celebrity by name was not a trademark violation.