I can't of course say that every startup company has this sort of culture, but my impression is that most small tech companies in startup hotbeds lean in the direction I describe. The sort of startups that catch my attention seem either to have such cultures or be straining to have them. They seem to think that hipster/dorm atmosphere is important for recruiting (the kind of people they want – 23 year-olds) and actively strive to create, maintain, and advertise it.