Adobe quote "tax reasons" as the reason that they can only accept payment though certain countries.
For example, I live in UK and I cannot pay for Adobe products through their American website; I have to use their UK site. I cannot pay in US$, I have to pay in £-Sterling. This is so that the correct tax is charged on my payments.
It used to be the case that you could purchase through the American channel if you were paying with a US credit card, irrespective of your physical location. I think that loophole might have been closed but it is maybe worth checking. There was also a loophole that involved purchasing via Amazon but I am not sure if that is still open.