Amazing how quickly time marches on. Thirty years ago, Letterman was daring, edgy and hilarious, some of the most outrageous comedy on the air. He also wasn't very popular. Maybe success has dulled him over the years. Maybe his writers aren't what they used to be.
But I agree with others: #1 was right on the money.
30 years is a loooooooooooooooooong time.. he must be just tired...