I am a huge Quora fan and user but would have to agree with this assessment. Most of Quora's traffic "lurks" and this will be the search audience they need to get. What they're doing now is trying to make sure they have your account credentials to monitor what you "lurk" for. At some point, my guess is that they'll remove this tactic. I will say, however, that the web created "inside" Quora is some of the richest, most high-fidelity information on the entire web, and it may not exist elsewhere.