What do they do with the cards that are never redeemed?
If the gift receiver never redeems the card, then it is like stuffing cash under your mattress. The store loses nothing, the gift purchaser still has the satisfaction of giving a gift, and the gift receiver can still redeem the card until the store either goes out of business, ends the gift card program, or upgrades their system to the point where the cards are no longer readable by their technology.
The only real cost to the store is the materials cost of the gift card, and whatever wear and tear there is for encoding the card with value. I would consider that an SG&A expense, the cost of doing business.
-PJ
Too bad the post office does not offer a "money card" much the way they offer money orders.
Why not just give cash?
A $50 home depot gift card is the same as $50 in a home depot holiday card?