So have I, but I've also tried on numerous occasions and being refused, due to my location. That's with Adobe + Canon products BTW.
This is precisely the point which needs more clarification. There are many US retailers who simply don't do overseas business. They have no 'country' options in their check-out section and no overseas freight options. In such circumstances, it's not surprising that they would refuse to do business with you.
However, it's an entirely different matter if a company like B&H who does
ship to overseas customers, says 'sorry, we don't ship Adobe products overseas'.
Have you discovered any instances of this occurring when you've attempted to buy Photoshop from America?
Well I do, returning stuff to be repaired on another continent with the extra delays involved is a pain.
Of course it is. As the saying goes, there's no free lunch. But how many times have you bought photographic equipment that needs repair within the warranty period? If the item is defective on receipt, I think it would probably be simply replaced, which is still a pain, but any item that is defective has to be returned to the supplier wherever you are.
Most products don't and Canon lenses being international is a new thing, if indeed true.
I can attest to the fact that it is indeed true. My warranty card for my recently purchased 17-55/2.8 lens in Bangkok has a title in bold black letters, "Canon International Warranty Card". It's in for calibration at the moment, in Australia.