Exactly. I work on security for a major retailer, and people try to screw the system with gift cards all the time. It doesn't work.
Those cards get activated (i.e. added to a database of purchased cards) by software on the POS system, they're totally useless.
Try it - walk into a shop and these gift cards will be unprotected on the shelf. Copy the number from the back of a card and punch it into iTunes. Their value will add up to thousands of dollars in one shop alone - what sort of a company would sell cards with what would effectively be cash value without that sort of protection?
People steal these cards from retail stores all the time. The joke is that they just risked prosecution to steal a worthless piece of plastic.
Also, I think that's why big stores abandoned gift vouchers. They were stealable and copyable, but a gift card is database checked when you use it, so much much harder to fool a checkout operator with.