Semi-serious answer: Forums are better because it gives you a way of organizing raids on other websites. It’s much more exciting for you and 15 other people to pull off a domination of the top page of every current topic on a competing site.
Fully serious answer: The increased topicality and democracy that a forum structure offers can create a much more vibrant community. You’ve listened to filmspotting. Check out their forum site and you’ll discover that the hosted show is only half of the quality content available. They have a handful of forum allstars who fill a role similar to guest writers, and their content is magnified over and over by pages of discussion from whoever is interested in the topic.
I always find it interesting who uses forums and who doesn’t. Some of my friends that I would have thought for sure frequent forums I find out are confused that people still use them, while other friends I will stumble accross in the most out-of-the-way corners of the internet.
Personally I love forums. The one I use the most is rather small and no longer attached to anything specific, but I also use a lot of ones geared toward online comics and a number for some of the animals I care for (hermies, reptiles, fish, etc.).
I’m not particularly a fan of the ones that don’t use phpBB though; I usually end up abandoning those. :/ Every other kind I’ve tried is just not as easy to navigate and keep up with the topics I’m interested in. I’m hoping that doesn’t happen here though because I find it very exciting that Overthinkingit has forums now!