It's difficult to justify that perfectly good businesses can go out of business over Yelp (at least outside of huge cities). I haven't ever typed "yelp" into my browser (or found it through google search) and yet I'm a technology-oriented guy. Maybe it's where I live?

Whatever it is, I think word-of-mouth is not a case for suing unless it is artificially created. I don't know how many salespeople at Yelp carried the "extortion" sales pitch, but if it was more than a few individuals I think they do have grounds to sue. Comparing this to "mafia" is ridiculous though and truly shouldn't be publicized by any news outlet.