They clearly have a responsibility to return the most relevant links and in this case they've gone pretty far but in my opinion they also have a duty to do thin

They clearly have a responsibility to return the most relevant links and in this case they've gone pretty far but in my opinion they also have a duty to do things like this as negative as it may seem. What Rap Genius did is why SEO companies exist. I've never been able to tolerate them for the reason that, for a price, you can "game" the system and rank higher even if your content is no better. In the long run, this type of behaviour is dishonest and damaging. By making a great example out of Rap Genius I think they've put it out there very clearly that you will be punished if found doing this like this.