Tim Bray explains why he doesn't want to use a database with the comment system that he is writing for his blog. It turns out he's talking more about the publishing model, dynamic or static, than the data store.

Serving static files generated when you post something is much faster than generating the page every time a user visits, so you can handle many more concurrent visitors. I like the dynamic model, though, because I think it offers a better user experience. I used Blogger and MovableType before I switched to WordPress and the publishing step always seemed problematic. Site-wide changes required regenerating every blog post, which took a long time and was error-prone. Dynamic publishing doesn't have this problem and has a simpler mental model, too. If you need performance, you can use the WP-Cache plugin, although I'm sure it's not quite as fast as a fully static site.