Leaving aside stylistic differences (eg laid back vs boom bap, funk vs jazz, comprehensible lyrics vs iggity biggity) there are some real thematic and content differences, in particular the greater importance of things like the 5% Islam (Islam in general really) and Afrocentricism in New York hip hop, while LA hip hop has more focus on gang affiliation.
Obviously it is a bit of a stereotype and comparing Q-Tip and Snoop Dogg doesn't really get a comprehensive picture, but was there a major difference in the social environments of the black communities in LA and NY that this reflects?
I always figured islam and afrocentricism had a big impact on NY Hip-Hop because the Nation of Islam was a NY-based organisation. Did the Nation of Islam have a strong presence in LA? Any users knowledgeable on the civil rights movement?