Heh, I took it to mean stars who maybe participated more in the show than others, or that one or more of the Muppets made a big deal out of. I haven't seen a whole lot of the episodes lately, but I know Piggy made a big deal out of Christopher Reeve's appearance, and he was in most of the sketches on the show. I don't remember him doing much else with the Muppets, though I know he was on Sesame Street sometime in recent years. Elton John's another guest who I never remember doing anything else with the Muppets, but he seemed to have quite a bit of airtime with 3 1/2 songs (one of them he sang a little bit of in his dressing room, but I forget which one at the moment). Though maybe Chris and Elton were just good examples of guests having more fun with their appearances vs. having much of a relationship with Jim or any of the other performers.