defining music genres is tough. Take R&B. Rhythm and Blues. When I think Rhythm and Blues I picture heavy on guitars, some piano, maybe horns... with a.. ahem, blues tint to it. The most mainstream I can think of would be Stevie Ray Vaughan.... or going back some of the Stax stuff, or even the Paul Shaeffer Band on Letterman. But the acronym R&B is definitely not that. Not saying it's no good but to me R&B is your softer black voices. Different audiences.
In the country music PBS doc you saw the difficulty in the 60s on people like Johnny Cash, Bob Dylan, and Kristofferson... country? Folk?