The word "nigga" is largely an American sociological and cultural issue. It's not about poverty. It's about Black people IN America where a white girl FROM America said nigga IN America. You get the point. The notion that Black people use the N word in London is irrelevant to what roaches is pointing out.
Also, saying that the word "nigga" is largely a matter of ebonics is a huge disrespect to a significant amount of Black people (not just impoverished in the hoods) who are against the word's usage and hate its ubiquity in rap culture. Many Black people have given me a "pass" for dropping the n word here and there (in a joking way), but that doesn't make it OK for me to do so. I still felt bad (when I sobered up).
Also, again, it's blown out of proportion. Kreayshawn doesn't readily use the N word. I haven't even HEARD her say it. It's only she posted it on twitter, quoting a lyric. V Nasty says it, but she's not White, she's like half Black. But let's not get into the whole thing about who has the right to say the n word. Personally, I think no one should be saying it.