Comment by justindocanto

I'm guessing it would be cheaper and/or more profitable to run their own ad network than it would be to pay for running ads.

Think about how they've turned expenses into profit in almost every other aspect of their business.

- Shipping their books? Ship their own + others and make a profit

- Hosting their website? Host their own + others and make a profit

- Advertising their products? Advertise their own + others and make a profit.