No matter what one thinks of Yelp, they were one of the first few place review services around. Then Google tried to buy them and, when that failed, copied their business model and turned it into Google Places which held top place in any location search.
I'm failing to see the problem. That is how competition is supposed to work: doing something better than someone else.
Did Google threaten anyone, or did Google just provided a better service/experience?
Did Google conspire with other companies to put Yelp out of business?
Did Google somehow leverage a monopoly position in search to gain a monopoly position in reviewing stuff?
As far as I know, Google is just a better competitor.