It was a correct move to make. With so little of the cards in circulation and with a even smaller player base having them/money to afford them, it would give way too much card and deck advantage to players who can get them.
It does open up the question of what will happen at Worlds. Perhaps there it becomes acceptable to them since there will be fewer players contending for the Japanese version at that point, but the possibility is there.
I don't see those cards being banned outside Japan since there were so many more of them printed in English (all of the top cut ones and the staff ones). Yes, those cards are still hard to find and expensive, but they're far easier to get in English than Japanese.