Matt Legend Gemmell explains why he turned off comments. I liked this part:
I want to make it clear that this isn’t a means to discourage conversation; indeed, I hope the opposite is true.
Comments seem like a relic of the pre-Tumblr era, when starting your own blog was actually a bit of work (and usually a minor expense). These days, if you have something to say about what someone wrote, you have many great options that don’t cause unnecessary work for the author or degrade their site.