in my case,you are right,its actually 30 days with receipt,which i have,although if i bought it in the states on 10th october,i could take it to regents street on the 9th nov and get a full refund.
if you read the terms and conditions,apple opened up a can of worms for itself as it wants to be a global "unibrand",in other words,you buy an ipod in new york,you fly to london with it,decide you dont want it,take it in to your local apple store and they will replace it for you,fact.
your receipt will be in dollars but the credit card that you use will be used to credit you back in pounds,reflecting the banks exchange rate on that day,and the bank's comission for the change.
Not sure how it works with cash,but thats whats happened to me before.so although yes,you are right,the 30 days will run out for me,the principal is still the same.you buy in tokyo,you take back in washington!
that goes for any apple branded product in any apple store,and as you arent compelled by law to get an at&t contract when you buy an iphone in the states anyway,you can,as with any apple product,exchange or be refunded.anywhere in the world.