Different currencies. The owners of Quora are being paid in US dollars, the content creators in both attention and reputation. Both attention and reputation are currencies that will translate to dollars more and more as we progress towards an, in-part, reputation-based economy. With everyone having access to information what will matter will be your curation of that information, and your commentary. The better these are the better your reputation will be in those content areas, and the more your endorsement will be worth (in both reputation and dollars).