Yeah, I'm not sure how big of a wrestling fan Letterman is/was, but back in the 80s on his Late Night show on NBC he seemed to have several wrestling guests. Killer Kowalski for one (
and
). Also Andre the Giant, Bobby Heenan, and probably others. Letterman grew up in Indianapolis and the story goes the nickname for his house band on the show, Paul Shaffer's "World's Most Dangerous Band" was a take-off of Dick the Bruiser's "World's Most Dangerous Man/Wrestler" moniker.
Basically CBS, NBC, ABC and Fox would be the equivalent of BBC1 and ITV, the channels with the biggest audience and (excluding Fox) longest history.