Blogs are fundamentally different than fora, in a couple of important ways.
*The blogowner sets the topic and tone, the commentary is secondary in priority, often being isolated from the main site by a link.
*Topics have a time limit on them, once they get pushed "below the fold", comment interest dips pretty quickly. Usually, anything of substance gets said in the first couple of days. It's pretty rare to get a comment on a stale topic, because everyone knows that replies are unlikely.
*Moderation is not obvious, and can be quite invisible.
*The content of the blog is the blogs "product", so to speak, people judge the blog mainly on what the blogowner has to say, rather than what the commenters have to say.
Here's an example:
http://www.redorbit.com/news/display/?id=747011
It's a science article discussing recent evidence supporting the "one giant meteorite" hypothesis of dinosaur extinction, compared to the "swarm of many" hypothesis. The commentary is entirely OT, degenerating into a typical evolution v. creationism by way of sauran extinction via Biblical Flood train wreck. The unruly commentary really doesn't impact my assessment of the site itself.
This is distinct from a forum, where the product IS the commentary.
* I also believe that the points concerning the overal maturity and gravitas of most of the denizens of Volokh are valid. Esoteric points of law simply doesn't attract a general crowd.