@simonwoods An interesting topic to be sure. I agree it can’t be a question of underlying technology. In some cases blogs are simply static HTML files. But I’m unsure it is simply a question of business model either. Many bloggers make money with ads.
I think in the spirit of a blog search engine what you’d be looking for in the decision process to add a blog would be that the site is run by a single person. Making it a personal blog. Sure, that person may hire someone from time-to-time to make an update to their site’s technology, code, back ups, etc. but by-and-large the blog’s content would be published by a single person.
Then again, this would eliminate great blogs like Kottke since he often has other authors.
Our rules for the 9rules blog were more around the layout and consumption of the content; is it a reverse chronologic index of posts? Is there an RSS feed? Etc. But I don’t think that model fits for the entire Internet.