I read the comments, some were a bit negative side about Quora introducing advertizing, others were quite positive about Quora itself and then a thought occurred. I haven't read it as explicitly as I'm about to say, but you know what the most popular startups and companies are really disrupting? Advertizing Google, Facebook, Twitter, Quora, Stackoverflow (a lot more niche though) are all making money with advertizing…
This is also why Snapchat has a billion dollar valuation [see how many views they send Buzzfeed http://www.businessinsider.com/buzzfeed-gets-21-of-its-traff...]