I'm guessing the restriction about the USA and Canada is most likely to have something to do with the possibility of paying money, so my guess is that as long as I'm outside North America I can't get them to send me money no matter what I do.

In principle the money isn't the main point (it's not that much anyway), but now that their T&Cs have annoyed me I find I'm inclined to stay annoyed on general principle...

They ought at least to give other people the option of payment in ThinkGeek vouchers or something.

I think it may also be them not wanting to bother with non-American IP laws (e.g. not wanting to get into the whole continental mess of "droit moral")