I'm from the south (US Southeast) and I would never invite myself over, but I've been to hang outs at the vast majority of my friends' places. On this topic it's barely even guess culture here - more like assume! We're still a very sociable culture, we're just a somewhat high-context one. For example, we had a friend who never invited us over despite dozens of hangouts at our place and others. We always wondered why he didn't view us as real friends. It's an expectation for close friendships here, even if you've just got a studio or place you share with roommates. Just part of knowing each other.