1. Click links to a website that come up while searching for something or reading other sites 2. Notice that you are starting to see consistently good results from that particular site 3. Start to go there directly for content, and maybe even sign up & participate
For Quora this is what happens:
1. Click links to Quora that come up while searching for something or reading other sites 2. See the blurred text, immediately click the back button 3. Start to equate Quora links with this mini hassle, stop clicking on them
Maybe their content is fantastic, but it is very unlikely that I will sign up for a site of this type that can't prove that to me first.
If, for example, they plan to generate revenue by selling leads based on individual's browsing histories, then they need view-only users to have accounts. In that hypothetical case, it wouldn't be terribly surprising if they found the expertsexchange model to be a good fit.