Can you buy songs and films from itunes different stores?

Hi i was wondering if im in the uk can i buy songs and films from the american itunes store. Its just when i clicked a link for a film and it directed me to itunes it said something about it wasnt in the uk store but in the united states store and so asked do you want to switch stores i clicked yes and i found watchmen the directors cut on there and the option to buy in dollars. would i be allowed to buy it or are there country restrictions it would seem stupid as the normal edition is in the uk and i really wanted to see the directors cut as well as buy some songs which are not available in the uk.