I'm more thinking about the social side of things. When comments follow the pull model, you get the pingback problem of old: most "comments" will be links to blog posts, themselves stuffed with more promotional links and so on. The only way to avoid it and have comments look like a somewhat nice garden is to allow post authors to say: please write text comments and don't stuff them with links, or you won't pass moderation on my blog. In other words, the push model. In my experience that's the best solution to this particular problem.

I think that's an issue of tools at your disposal to create content (including comments) rather than their distribution model (e.g. pull vs push). If your main method of saying stuff is through a blogpost, ofc you'll end up in the situation you've described. If the tools at everyone's disposal are textboxes that just work, people will use that.