it's actually not - Matt Cutts specifically made a video about these exact type of "widget" links a few months ago. He recommended that they be no-followed.
Rap Genius was given a "manual action" aka a penalty applied by an actual human because of the public outing that happened over the past few days, and the attention gained specifically by Matt Cutts.
Their overall link portfolio is not half as bad as their competition, however all this attention forced Google to take action being that they need to live up to their reputation as hard asses.
Let's face it, the algorithm might not pick up on these bartered links because they are a drop in the bucket of their overall link portfolio.
Really more than anything this is another PR stunt by Google's search quality team. They have been outing people on Twitter for the past month (backlinks.com I believe and another blackhat service) and want the general public to know that they mean business.
