... I guess Stardock thought it would be beneficial if the different "local" communities mixed a little more. ...
It can still get messy, even with the source-site info in the UI. The folks at Wincustomize seem considerably less comfy with trash talk than the gamers seem to be, not just 'swear words' but even 'clean but mean' talk.
My GC2 friend Mumblefratz actually attempted to map the forums a while back, but I can't find the post I'm vaguely remembering. If you're ever curious about what other sites might share a topic you're in, just replace the core domain name, elementalgame, with another Stardock site like galciv2, impulsedriven, wincustomize, or joeuser.
This topic is also available at impulsedriven and stardock, but not at wincustomize or joeuser. (You'll almost always see the thread when you play this game, but you can tell it isn't locally available because the topic name isn't displayed at the top of the page.)