David LettermanEverybody knew it was coming. Some thought it would be last year, when he approached Johnny Carson’s record for late night longevity. But David Letterman sailed past that milestone and continued into this year’s complicated changing of the guard on competing stations. Letterman acolyte Jimmy Kimmel had moved down to 11:35; and longtime rival Jay Leno, who got the “Tonight” show job he coveted, was finally gone.

Letterman, the survivor, had won. And so he figured, not quite out of the blue this week, that he really wasn’t that into his show any more. And turning 67 next week, he figured it would be time to say, yeah, he was going to hang it up. Next year some time.

He gave his typically low-key, chatty explanation in a round-about segment between monologue and first guest Thursday night — a form he had long since mastered. It was in such a segment, also out of the blue, that he got ahead of a wild blackmailing  scandal by admitting he had cheated with a longtime production assistant on the show (not one in the background, but one who was quite prominent on the show). He also spent time to talk about his own heart operations, tried to heal the city after 9/11 and generally kept his goofy, mostly good-hearted humor through the years.

In recent years, he wasn’t quite into it. But that was part of his charm. He liked talking to starlets well enough, as much as anybody would, but he wouldn’t pretend to be part of their hype machine or even admit he’d see their movies. (His best guests were not much different, Johnny Depp on Thursday seemed downright embarrassed at his latest film and said he hadn’t seen it).

Compared to the over-eager Jimmy Fallon or the overly-cynical Jimmy Kimmel, Letterman was somewhere in the middle, closer to Carson than either of them. In fact, it was on Letterman that Carson made his only post-retirement appearance, just to wave. He also wrote jokes for Letterman that he’d send in right up until the year he died.

When Letterman got one of those lifetime achievement awards a couple of years ago from the TV Critics Association, he didn’t show up at all, but sent a tape that said he was sorry, this was the weekend he’d set aside for eating glass. He sent an impersonator in to run in and get the cheesy trophy.

In a way it was perfect — just what you’d expect from Letterman, who pretty much disdained the trappings of showbiz since the time he hosted the Oscars (considered a flop at the time, I bet it would hold up pretty well today).

Letterman was criticized in his time as being the kind of guy who ushered in a generation of snarky kids who didn’t feel passionately about anything; for whom irony was king.

Letterman himself wasn’t like this; he cared about his family and especially his son, now 10. When he got presidents and candidates on the show, he was fully engaged and even agitated in getting serious answers.

No he wasn’t one who jumped on every gimmick, who is desperate to connect on Twitter or collect views with YouTube ready filmed bits. He was old fashioned that way. And there was more room for messing around in his show — or for lamenting how poorly things were going — than in most.

He as grumpy and aloof at times, but real. Every time you invested a few nights in his show, you’d get caught up in the rhythms and running jokes that would make the time worthwhile even if the guests weren’t.

Letterman won’t be good at the year-long farewell. He got embarrassed enough by the fuss the studio audience raised Thursday. He’ll have a moment or two of real emotion before he gives his last wave. But he won’t lay it on.

I can’t even imagine what kind of replacement there will be. Louis CK went through the tryouts to replace him in a fictional segment on his own great show, but he’d probably be a bad host. Jon Stewart and Stephen Colbert, working on a Viacom property, would be judged too political. Conan would represent a step back in a way, and is probably too similar to the Jimmys surrounding him. (But really: I can’t conjure much more interest in the topic than Dave probably has)

The sure thing is this: when he’s gone, nobody will come close to matching his longevity, and there will be nobody around like him.