NBC (Yes, NBC) Wanted Letterman Back

It's pretty clear that NBC still doesn't understand David Letterman. He'd have come running for the "Tonight Show", but that's not what they offered. They offered a prime time slot, four nights a week, every weekday except Thursday at 8 PM ET, 7 PM CT. The thing is, they offered him a prime time slot ten years ago and he turned them down then because he didn't think it would work. Why would they think anything had changed?