That right there: bingo - that's why I think that Yelp is coming out on top of this. They're delivering value to the website visitors/app users. Not that either company is a paragon of virtue, but compare Yelp to Apple and yourself to an iOS app developer and I suspect you'll have an accurate picture of who's where on the totem pole (cf Gruber: http://daringfireball.net/2010/05/nack_control ).

If Yelp were dedicated to making its advertisers happy, it would quickly become useless for its users.