It sounds like Stardock only has North American distribution rights, while
Gamersgate has the UK, at least (they don't list the price when I check that page, and if I click on 'buy' I just get a message that it is not available for purchase from my location).
Did you try contacting Stardock? There may be a time limit on the region exclusivity, but if so I would expect it to be on the order of a year or several.
