I'm afraid i diagree with James. The idea of listening to a certain type of music to fit in can be applied to ANYTHING (i bet you there's someone in a rap forum saying how pathetic it was when he used to listen to cheesy heavy metal where skinny old men wear tight leather trousers, with crap lyrics and little beat to it, just so he fit in with the kids who like that stuff in school) .
I agree with Rask (again) about the cross pollination of the genres.
Zepp-rules: can i ask who you've heard? cos the discription you gave there pretty much hits radiohead's "idotique". It's not all was about achiving a certain melody there is a poetic element in there. Rap and playing the guitar a very different things, you cant apply rules from one to the other. If you think it takes not talent try it for your self (i did), it's certanly harder than it looks.
The idea that a guitarist (from a genre you know lots about) doesn't get famous, but a "random" person (someone from a genre you don't know too much about, so you somehow think this is because they dont work hard, as opposed to you not knowing about them) gets famous isn't really the most realistic of ideas.
I'd just like to point out that the mainstream rap at the minute isnt the best it's been.
To be honest i think sometimes when we hear a song that sounds good by a band we dont like, and so we tend to have something against the song, which doesn't really make anysense, cos at the end of the day a good song is good song.
(Sorry about the length of this reply)