I believe Quora is taking the Facebookian view of going overboard with privacy issues, then pulling back iff users revolt. It is, technically, the best way to push social interactions as far as possible, especially if you are not punished for temporary lapses in judgement.

Users WILL NOT actually punish Quora for stunts like this, so, from the company's perspective, it's a good bet, temporary bad press notwithstanding.

I remember successfully arguing down a similar bad privacy decision at another well-known company I once worked for. It took a treatise on social software, including multiple citations of other social snafus, the painstaking gathering of stakeholder acceptance, and a near-fanatical perseverance to stymie a feature that was absolute poison to our privacy model. The guys at the top were happy to launch-and-see. I suspect that's what's going on here.

tl;dr - For this to get out at all, either Quora's process is broken, or their strategy is to overshare and pull back only when necessary.