George didn't handcuff himself to Letterman because he's not among the guests on the TV veteran's final show next week (we'll get to the line up shortly), rather that he just doesn't want Letterman to leave, period (as the Americans would say). That and he's just into handcuffs, for an array of reasons.
As for who is confirmed for next week's final show; according to reports Eddie Vedder, Tom Hanks and Bill Murray will partake in Letterman's final line up. If you thought Julia Roberts had been on the show countless times having appeared on 26 occasions, Tom Hanks has been a guest on Letterman SIXTY TIMES. Bill Murray has chin wagged with the 68-year-old host a grand total of 44 times.