It's a question of where you want the conversation to happen and whether you want to encourage this conversation in the first place. There are plenty of (successful) sites that act merely as a megaphone for whatever the author has to say, while he doesn't care about what random readers think. Meanwhile, lots of blog authors pray for some kind of feedback, some kind of legitimate comment that never comes.

Providing a comments section or forum builds a community around information sources that are already valuable and/or have a high reputation. It seems a little short-sighted to miss this opportunity to build a relationship with your users that goes beyond satisfying their immediate needs. People have no loyalty to their information sources, they'll switch when something better comes along - but they do hesitate to leave a community, even a stagnant one.