I was sitting in a meeting this morning trying to stay awake, when the beauty of Google's business plan dawned on me. They sort information based on links, and ads are treated as a link. So, they have created a mass incentive to advertise on the web. Now suddenly, the more you advertise, the more google references you. Specifically, the more google will refer to ads you place on their website.
They are essentially single handedly creating the whole source of their revenue from nothing, but in a very intelligent monopolizing way. And the best part is, they're sharing the wealth with other websites. They're like a big advertising symbiote.