> Different currencies. The owners of Quora are being paid in US dollars, the content creators in both attention and reputation.

I think this is spot-on. I answered questions on quora for a while, but eventually left once I realized I was getting nothing out of it besides (some) "reputation" on a closed-off website. The reputation (and any associated ego/self-esteem boost) might be enough of a reward for some to justify continuing, though.

> Both attention and reputation are currencies that will translate to dollars more and more as we progress towards an, in-part, reputation-based economy.

I am not sure this is or will be univerally true. It does work for some people, though they seem to be a minority. Not every twitter-celebrity can convert that status into a way to support themselves financially.