"Reddit has an inherent problem in that the only people who are moderators are the people with the time and inclination to be moderators. These people tend, to borrow the previous language, to be below average in certain dimensions."

People often say that HN is as good as it because of dang. So perhaps there's a lot of correlation between community quality and moderator quality, and how good moderators don't just happen... you have to filter and hire them to some extent.