http://rapgenius.com/Jay-z-somewhereinamerica-lyrics#note-19...
Jay-Z is fairly well known to have reached considerable wealth prior to Reasonable Doubt. The 'Classic Albums: Reasonable Doubt' doc covers this quite well. The route of selling 'In My Lifetime' out of his car was one in turn that he escaped.
This is not in contradiction with your quote.
Sean Combs (formerly Puff Daddy), Jay-Z and Dr. Dre come to mind immediately.
I'm not sure if I'm misunderstanding your point, but all three artists reached business success through hiphop. Jay-Z was selling mixtapes out of his car to get enough recognition to release Reasonable Doubt.