hmm, but i think there's wider forces that dictate what they cover (esp given how their circulation has shrunk over the past 20 years) - if the kids want indie, then commercial logic dictates that's what they'll give them. They tried including black music, and I assume it simply didn't sell to their demographic, so they stopped.
The first time I bought NME it was when Def Jam was on the cover. I think NME at the time reflected the sense of excitement about the hip hop crossing over in this massive way - it also tried to reflect the rave years etc. I think it's right to say it reflects a wider cultural seperation - a class/economic seperation as well, being indie's demographic is the middle classes. A bit sad really.
It also makes me conscious of how much I don't give a shit about most of the music in that chart. I've only heard Jay Z, Dizzie, MIA and Johnny Cash and imagine it'll stay that way.