All this talk about dissing rappers about their blings blings and their subject matter applies to most musical genres...
I mean, these rappers will look at the emo kids and go like "Yo, only 'em bitches wear 'em MAC make-up and eyeliners." or look at the black metal scene and go, "Wassup with the chains and collar spikes, dawg? Tryin' to look like one?"
Every music subculture has its certain image and accessories which its own following identifies it by. And quite a fair bit of people follow a certain music genre due to the fashion statement it makes. Even the hardcore scene does in a certain way with those 'X' marked across their hands. It's called branding...
Rap/ hip-hop started back in the 70's with a stronger socio-political message in the Bronx. If you are really interested in that, please Wikipedia it. And hip-hop production is fucken amazing. I love it. The amount of layers in the music is sometimes more than a boring rock tune.