I saw an interview with Clapton where he told how he tried to work out one of the more complicated songs and finally gave up realizing his fingers weren't long enough to reach all the notes Johnson was playing in the same chord position.
Plus, Clapton sucks.
It was the realization that, in order to play a tune like Johnson played it— it would require the rest of his life to get the intonation, timing, and tone. Ie. not possible. There are a number of tribute players who have made it their life’s work and done a remarkable job- he was one of a kind.
Two tracks, an interview with Clapton “a life’s work” to try and copy Johnson, and highly complimentary (and NOT taking anything away from Clapton who is a devotee, like Billy Gibbons, of Johnson) and Delaney and Bonnie Bramlett (with Duane Allman) live from a while ago- great version of “Come on In my Kitchen”
Clapton: http://www.youtube.com/watch?v=ETELORdwmJA
Delaney and Bonnie: http://www.youtube.com/watch?v=3uzEH_Cy0ew