The whole point of this penalty is that Google cannot trust the signals that are in its index when it comes to Rap Genius's site. And it sure isn't Google's fault that they can't.

Can Google subtract out all the "naughty stuff" and decide if Rap Genius deserves to even be on the front page for "rap genius" anymore? I doubt it.

If Google's search had a category for "obvious searches" then yes, maybe they could apply a penalty as delicately as possible. But delicateness is not really the point. Dropping them down 50 spots is blunt and simple. I think everything about this approach makes sense.