Direct sale is an excellent model but I don't think it's a requirement. To me it underscores the main principle which is about reducing dependencies. Why convince two parties to do something (someone to visit your site, and an advertiser to run an ad targeting that visitor) when you can convince one.
I'd also add that the single most important thing I've found in creating a business like this is keeping your costs low. The same two businesses, with the same income and customers will have very different times during a downturn depending on their committed monthly burn rate. I know it sounds obvious, but its amazing to me how many businesses handicap themselves from day one with large spending commitments.
I'd also add that the single most important thing I've found in creating a business like this is keeping your costs low. The same two businesses, with the same income and customers will have very different times during a downturn depending on their committed monthly burn rate. I know it sounds obvious, but its amazing to me how many businesses handicap themselves from day one with large spending commitments.