He didn't make the comment on MNF, he made it on a news talk show...completely unrelated to football or music and with absolutely no affiliation to ESPN or ABC.
But, I guess the First Amendment doesn't mean what it used to anymore. If you're employed by ESPN/ABC, you can say whatever you want anywhere you want, but only as long as ESPN/ABC agree.
Edit: What's really funny is that Williams Jr. isn't even really employed by ESPN/ABC...