A friend recently defended his dissertation, the last phase in his twenty year process of getting a Ph.D. He is now a "doctor." Nothing conveys authority like having a Ph.D. But who says that he is an authority?
As it turns out, very few but very learned people say so. Who says they are learned? Another generation of a very few, very learned people. And so forth.
I learned something that surprised me: anyone may participate in the defense of the dissertation. If I had wanted to take the time and effort, I could have gone down to Penn and thrown my own two cents in about late Roman history. I could have started a brawl, jumped up and yelled, "oh that's no such thing!"
This is also true for Wikipedia: anyone may participate. But they don't have to take the train downtown and find room 202a in Whoosy-flop Hall. Nothing impedes participation. And apparently, everybody wants to participate.
So while the Ph.D. process depends on the knowledge and review of very few, very authoritative people, producing very authoritative work, wikipedia depends on the knowledge and review of very many people who are anonymous, and therefore have zero authority. So zero authority multiplied by a large enough integer equals ninety-nine percent accuracy?