Do you mind if I ask where you're from in the UK? I find that there's an awful lot of variation between different regions. For a few years now, I've lived and/or worked in London, where chatting to strangers is not the done thing. But travel to certain parts of the north of England, or Scotland or South Wales, and the norms are much more like what you describe in the US. My father was from South Wales and he loved visiting the States, where he found people to be open and friendly and willing to chat, just like they were where he grew up.