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?