Comment by andrewaylett

It is, however, literally worth that amount of cash at the moment of redemption. If you were going to spend that money in that shop anyway, and you have no intent to sell the card to a third party, there's no need to apply a discount.

It's not all that surprising that "just like cash, but less fungible" should have a different valuation than "cash", but there aren't all that many things that mimic cash like that.