I am guessing the reason they aren't putting ads on Quora yet it would limit their ability to raise money. Uncertainty drives the theoretical value higher because while the average CPM on ads might be say $10, they can project because of their higher quality content that they will be able to charge $25 or $50 CPM or something like that. So, they can sell projections and vanity metrics instead of actual revenue to investors.<p>Also, not having ads means they are totally product focused, not focused on ad sales and driving up their ad rates. That helps them keep their team small so they don't burn through money hiring to build up and sell their own advertising system.<p>Last, not putting ads on their site insulates them from the ups and downs of the advertising market. If ad prices drop one quarter, their future projections have to change a lot because of the real numbers.<p>Long story short, I don't think if Quora put AdSense on their site that they would have been able to raise $161 million dollars.