In reply to The New NickB:
> Maybe that's where it comes from, it's easy to forget that the US's German roots are just as strong as the more famous Italian, Irish, English, French roots.
Apparently it came from the auto industry trying to shift the blame for cars killing pedestrians to the victims.
http://www.bbc.co.uk/news/magazine-26073797
As others have said, just because something works in the US, doesn't mean its appropriate in the UK. My experience as a pedestrian in American cities has largely been poor compared to European standards (Atlanta probably the worst, Portland almost civilised) and I certainly wouldn't want to strive to emulate that. Especially when you see that they have a road fatality rate several times that of the UK (around 35,000 people killed a year - which is mind boggling really).
That said, I think too many car drivers see green as a go and red as stop (usually) and switch off some of their personal responsibility. When you allow turning right if clear, you force (hopefully) the driver to take a more active role in checking their surroundings, rather than just coasting through because it's green. Its similar logic to removing road markings etc in shared use streets.