bo used the same riff over and over as well, so did the stones (satisfaction / jack flash), muddy waters had his own riff too which he re-used constantly, these guys werent thinking in terms of originality, they were playing to entertain mostly black audiences at dances, makin people shake and hollar was their currency. then they crossed over with a little help from elvis. but the thing is the sound they created was the blueprint for rock n roll