Media Matters notes this from an interview with Williams on CSPAN's "Q&A":
WILLIAMS: I do listen to Rush. I listen to it from a radio in my office, or depending on my day, if I'm in the car, I will listen to Rush. And he will tell you I've been listening for years. I think it's my duty to listen to Rush. I think Rush has actually yet to get the credit he is due, because his audience for so many years felt they were in the wilderness of this country. No one was talking to them.... So I hope he gets his due as a broadcaster.
Had Williams said the same thing about, say, Tommy Chong, he'd be summarily fired, then flogged with a skull bong. Nevermind that Rush is a serial racist, misogynist, and liar. See Media Matters for a brief list of some of what Brian Williams is megadittoing.