UK citizens pay more because they are chumps. I don't mean that in such a negative way, what I mean is they are TOO NICE. Seriously, studies, which I don't have links to, have shown that UK citizens will tolerate bad service, shoddy merchandise, and higher prices.
US citizens however, demand refunds if the product/service comes up even a little short of their expectations.
There are other forces at work too, regarding pricing, but really, US citizens will throw an absolute fit if they feel prices are too high. Heck, we will throw a fit just because we know we can get the prices lower, or get better service.
Naturally that will not apply to all US/UK citizens, but the study I read showed a tendency.