Bill Maher wrote a dead-on-target piece about Johnny Carson noting — and it's hard to believe it's been this long — the 20th anniversary of Johnny's retirement.

He is quite right about Carson being ruthless; about how Johnny wouldn't hesitate to cut off a guest he thought had worn out his or her worth to the show. I've made that point here before. Over at the official Carson website, they used to have an online database of guests who'd been on the show and the dates. You could look up any of a long list of guests Johnny once had on often — Tony Randall, Charles Nelson Reilly, Jaye P. Morgan, Charles Grodin, Robert Blake, Orson Bean and many others — and you'd see the person appear every week or two for months and months —

— and then suddenly, nothing. Johnny would just decide the guest was out of funny stories or the guest had gotten too familiar or something…and they'd be gone. No sentiment.

I also agree with Maher that Johnny wouldn't fare so well in today's competitive marketplace. I love Carson and think there'll never be anyone like him. But I still think he left when he did because he knew that his act was running out of steam and that if he didn't go out soon, he wouldn't go out on top.