For the most part you're right, but sigforum is pretty decent.Unless I need something specific, I try to avoid forums dedicated to a specific gun type, manufacturer, etc (ar15.com, GlockTalk, et al), mostly because a lot of the regulars tend to be serious a**nozzles if you don't conform to the prevailing opinion.
I'm a member on quite a few different forums, but there's a reason I'm on here nearly everyday and only rarely check the other forums.