I found an interesting article that compares Google and Facebook, including their advertising strategies.
Both Google and Facebook have been molded and altered throughout the years to benefit both the users and advertisers. This article gets in to how only reaching your fan base is the minimum you can do as a brand. In order to keep your fans, and gain the attention of new ones, Facebook believes brands need both a solid page and paid advertising. They hope this will create a cycle where both brand pages and ads bring in more consumers for the brand and facebook.
I think this is an interesting strategy and way of thinking. It gives smaller, lesser-known brands a chance to reach a lot of people even if they cannot pay for advertising at first. However, this will steepen the competition, and that brand will most likely pay for advertising eventually. Facebook also hopes this competition will bring on more viral ads.