Great comedy may be timeless, but that's probably because of the great comedians performing it as much as the material itself. Could you imagine Dad's Army being anything more than a shadow of its former self if it was remade with a new cast? Would Frasier achieve the same transcendent mix of bourgeois self-regard and millisecond farcical timing with James Corden and Mathew Horne in place of Kelsey Grammer and David Hyde Pierce? Do we want to hear anybody reciting the "Dead Parrot Sketch" ever again?