Yes, exactly. Impersonation isn't what's needed to take on a character. You have to know everything about the character. How it thinks, how it would react to a give situation, etc. David Rudman knew Richard Hunt well, so he seemed like a natural choice for taking on Scooter and Janice. Jerry probably knew Richard even better, so natuarlly he acted as a good mentor for David. And Jerry had said in the past that he chose Matt Vogel to take over for most of his characters because Matt seemed to understand him best. Same goes for Steve taking over Kermit from Jim. Though you could argue that it was a different story with Eric taking over Frank's characters, but nevertheless, Eric had already been around the Muppets for awhile. And as much as I hate telling people who so desperately want to become Muppet performers, and feel that they're suited for taking on already existing characters, they should know the truth.