I think UK users get a rough deal but not just from M$. Increasing it's a premium we can't afford to pay.
It's not as if they bother to change anything much from US to UK English.
Radical thought once upon a time but if the pricing isn't going to come down then depending on your needs instead of upgrading at the whim of M$ to windows 7 and office 2010 maybe it is time to seriously consider Ubuntu and OpenOffice.org.
I am sure the US price will be minus the sales tax which I believe varies from state to state whereas the UK price as we all know includes all taxes, and yes the US price will still be cheaper.