Every single time it's been very clear that Yelp is telling these businesses that they have a problem. But rather than acting on this extraordinarily valuable feedback the owners/managers react by blaming Yelp for the bad reviews or accusing Yelp of hiding the good reviews.
This behavior frequently exposes the characteristics about which customers are complaining: there's a problem, the owners have been told about it, and they're killing the messenger.
EDIT: I have no connection to Yelp whatsoever. I'm communicating the scope of my experience and the conclusions I've drawn. These conclusions may be grossly flawed. It wouldn't be the first time today. :)