and every game does have its own uniqueID.....but with gateway its easy to dump hundreds/thousands of uniqueID's.....that would be a cat & mouse game.....i dont think nintedo would want to go down that route unless it was a last resort, what would be ingenious for them to do, would be to trick people into updating, basically in the next update have the software to block the card, but not activate it for a while say 1/2 weeks after its released, and once triggered it stays so no changing the clock to unblock it.....if they where really smart they would do something like that, not only blocking the cards, but tricking users into updating as its confirmed working initially
but nah i think its most likely just them wanting to do more than a quick patch and needing to make sure it wouldn't effect any legit users