It's also interesting that the outliers -- the artists who derive most of their income from recordings -- tend to be rappers. Eminem, Jay-Z, Linkin Park (A little bit of a stretch, but close enough for me), and Brian "Baby" Williams are the ones that jump out at me.

This would imply that, rationally, rappers should be more concerned about copyright, and people like Billy Joel and Neil Diamond shouldn't care one bit.