Reruns, we’ve got reruns!

Question: When David Letterman takes a week off, why are the re-runs always episodes from about six weeks before? I mean, we just saw these! (As I write this, for posting Sunday morning, Dave is cracking jokes about Rush Limbaugh’s comments about Donovan McNabb.) Can’t they rebroadcast some really old episodes, from 1995 or so? I’d love to see an old interview of, say, Samuel L. Jackson promoting Pulp Fiction or some such thing.