The point is that using social status to motivate people who provide content or do other useful work is very common; it's arguably one of the defining features of what the press calls Web 2.0. Karma is just a (crude) way of quantifying that.

I first saw a similar quantification scheme on Everything2, an early competitor to Wikipedia that morphed into more of a writers' platform when it became clear that Wikipedia was winning. They called it XP, though.

What percent of YouTube uploaders would you estimate get paid more than, say, $1/month?

Volunteer organizations motivate and compensate their members in a variety of ways. Most of the ones I'm acquainted with do so via immaterial rewards, which was your original question.

With respect to the new goalpost of "karma points" -- can you clarify what characterizes the set of "karma point" like reward structures? If the Catholic Church selling indulgences qualifies, I'm not sure why wikipedia granting wider edit privileges wouldn't, for example... those things are certainly different from one another, but then again both are different from karma points. I'm not sure what differences are significant, on your view.

Hrm? As a scientific reviewer, you get the reward of being able to list "reviewer for XYZ" on your CV. Which is an "immaterial reward", probably about on a par with LW karma. Both are a mild point of prestige, but not really enough to boast about in isolation.