Another element of this is the fact that rappers, unlike "indie" artists, WANT to be popular. There is far less venom from the hip hop community for an artist who makes a huge hit partnering with a pop artist than there would be for an indie artist who did the same. If Radiohead teamed up with Ashley Simpson they would be crucified.

Indeed. Good point.

It might improve both Radiohead and Ashlee Simpson.

So would inoperable cancer. What's your point?