What they provided wasn't exactly 'proof'. Without any conclusive ground they accused other lyrics sites. Linking to Open Site Explorer and saying they they think some links might be suspicious hardly counts as proof, IMO. Besides, now that the matter has been brought under Google's attention, they'll of course penalize the other lyric sites too, if any violation is found. But in case of RG, it was all out in the open and I think that's why action was quick.

Their "proof" was a load of crap. AZLyrics has several lyric websites for specific genres (punk, metal, and so on) which are actually really good if you're a fan of that specific genre. Of course these sites link to each other because they're a part of the same company. It isn't anything like what RG is doing.