The first one in that list typically has as many posters as this forum, but the discussions are night and day. There's a lot more sharing of cool stuff or stories, a lot more asking of advice, a heck of a lot more pictures.
Here, there's a lot more debates of the rules. What the best X is, if class or spell Y is good or bad, Unearthed Arcana evaluations, stealth, warlords, and general arguing. There really isn't a lot of people just talking about their game, getting advice, or generally being excited (or happy) about D&D. It doesn't feel like a fan forum for a hobby people love. There's not a lot of joy in these forums.