Can you imagine if Stackoverflow did this? The tech world would grind to a halt.

So you're saying you're not upvoting useful answers on StackOverflow?

Upvoting alone is enough to make me sign in to SO when I'm mysteriously logged out. SO saves me enough hours to justify that small curtesy.

I actually am signed in, but I know a lot of their traffic is anonymous users.

Which is better for caching, so it has advantages

I don't know, in the case of StackOverflow I think it's worth the registration vs going back to pounding your head against the desk.

Don't give them any ideas!

Naw. Not signing up for Quora means you won't get to essentially entertain yourself.

People would immediately sign up for SO if it were tied to their productivity.

That is, unless answer providers have no interest in using the site for anything else. That's true in some cases.