The reasons you cite have absolutely nothing to do with the definition of music.
Perhaps, but if so then it's more like a 60% majority than a 90% one. The blackness of hip hop is exaggerated. For example, out of the most prolific hit hip hop producers in recent years (neptunes, scott storch, timbaland, missy elliot) who are responsible for virtually all of the top hip hop tracks of the 00's, 3 are black, 1 is white and 1 is fillipino. When you move away from pop it only gets more diverse. The lines between hip hop and other genres (particularly electronica and rock) blur considerably, even when looking at the top producers named above, all of whom produce as many hits for pop and R&B stars like britney spears as they do for pop rappers like 50 Cent.
The pop rap audience is actually overwhelmingly white in the US. Feel free to do at least minimal research before forming opinions.
Well, considering his california desert town is 90% white and 0.63% black and the demographic makeup is likely similar for 20 miles in any direction, I'm not sure whatever sample he's using is remotely relevant.
OK, but it's still a majority. What's the problem? Secondly, so I was wrong about the audience. That's why I labeled it a "guess." That's what one does when one isn't sure about something.