Windows Vista added the ability for software to be "geographically activated" (whereby you can only activate if you computer is in the right pricing zone). Previously this only applied to Home Basic's reduced pricing in SE Asia, but I imagine they'd do the same thing in this case: the lower-priced Windows 7 would be geographically locked to the UK for activation. I imagine Microsoft will downplay this to prevent the media miscontruing it as "you can only use Windows 7 UK Edition within the UK".
Can't this by bypassed by using a proxy server within the UK?