I think it's very regional within the UK. I grew up in the South-East and now live in London where it just Isn't Done to chat to strangers. But I've lived in other places in the UK where people are more open to it - in a small town in Scotland, even in a fairly large city in the South West, and definitely in the country-side in general.
But, as someone said in the other thread, the way in which it is done differs to the US (where I have been several times) - it's much more subtle. You wouldn't just say "Hi, my name is.. how are you?" or anything, you'd slide into conversation more subtly. If in a pub, you might say "Ooh, can't decide what beer to have, what are you drinking?" or "horrible weather, isn't it?" and see how the person responds