Rock And Roll is a pretty big umbrella...
For example, soul music can be considered a variation of rock and roll and thrash metal too...
However, you can't tell me Slayer/Metallica are making the same type of music as Curtis Mayfield/Isaac Hayes...
Hip Hop needs to develop the same categories...
Yes, it is all rap...but a song like "NY State Of Mind" does not belong in the same category as the "Motto"...
I am not saying one category is better than the other, but the music is clearly different...