> Isn't that an obligation when you own a trademark? That you sue people, or else you may lose the trademark?

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.

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.

I don't see how that matters. If someone is acting in your name, you best keep tabs on what they're doing.