Imo. There are very few exceptions to this. I've just never really cared to know anything about any of the rappers I listen to, bar maybe a very small handful. I never read interviews with them, or biographies on them, check out dvd's about them, or take any steps to learn more about them. Why? Because very few of them actually seem like interesting people. That's not to say that they're not. Just that I really don't care. This is reflected in the fact that only a miniscule percentage of rappers actually make interesting music.
On the other hand I have always been really interested in my favourite rock bands, and tracked down biographies and other books on them, as well as reading about them on the internet.
I guess if I was in a book shop and I saw a cheap autobiography of a rapper whose music I was particularly fond of, I would buy it. I wouldn't buy a biography written by someone else though, no matter how cheap. But I'm the type who is always picking up strange and unlikely books if they're cheap enough, so that doesn't really mean much. I would pretty much never actually pursue reading materials or information on a rapper is what I mean to say.