I think that is does benefit Quora for content providers to see how much traffic is being generated from their site. If I knew an article was getting a lot of traction on a site I would spend more time on there, perhaps participate and continue to improve and generate content itself, thus benefiting Quora with more data and more links for everyone.

Of course there is zero incentive for anyone to do it. And if everyone chose to link the way Quora does, you get a Google Analytics dashboard which cannot tell you what all URL's are sending traffic to your site/blog. I find it really difficult to imagine.

The long term effect would be that websites can no longer use referrer as a metric. What difference would that make? HTTP resources (webpages) shouldn't change semantic meaning depending on the referrer anyway. Doing so is arguably an unintended use (or abuse) of HTTP.

Absolutely! And see the funny reasons people have been citing in favor of such an act - http://www.quora.com/Why-does-Quora-redirect-to-URLs-in-a-wa...