Can $5 Improve Reader Comments?

Interesting question: Can $5 Improve Reader Comments?: On the Web site thatsaspicymeatball, you can view the latest comments from MetaFilter (which requires a one-time, $5 membership fee to post a comment) and YouTube (free) side by side.
The site’s creator, Bertrand, uses Yahoo Pipes to retrieve comments from the most recent posts on both sites and displays them on one page, which is updated every hour or so. Bertrand’s comparisons leave him wondering what drives the quality of a Web site’s comments: is it the membership fee, the age or demographics of the posters, or the level of comment moderation?