I think that one of the things these megagroups were so impressed by is the fact Johnson did break the rules whenever he wanted to. Yes, it IS a 13 bar blues, so? What are you going to do about it?
When Clapton recorded his Robert Johnson sessions , he was talking about the separation between the guitar parts and the singing parts : "I mean, to do those two things at the same time…until I….and I still can't do it completely right, I can kind of get an approximation , but it's almost one of those things…when you listen to it, it just sounds so relaxed, and yet when you come to try and do it you find out how almost virtually impossible it is."
Maybe it was the devil's gift after all…
One last comment about the whole devil story, just to prove again that with all dues respect, tom waits did get this one right…isn’t it strange that in order to sell your soul to the devil you have to go to the cross(roads)? Just saying….