I don't think you need statistics to draw that conclusion for you. Personally I feel safe to assume from my experience with the site generally being pleasant and informative that it is because nodes tend to be well written.

Or rather, I should say, not bad. As you saw from your analysis, the overwhelming majority of nodes end up with a handful of upvotes. To state it in a cold and detached way, that means that the average node is a tendentially better than entirely useless.

I like Perlmonks. It's a comfortable community of geeks.