I don't think it's "always" been there, but I found out a few months ago as I was researching how to get rid of buckets of coins without a fee.
Haven't tried it myself, but plan to for a future trip.
*** Remember that SW only takes up to 4 sources of payment for a single ticket-- so when you get your gift card, you may want to get at least $50 or $100 or so in value per card and not a bunch of $10 or $20 dollar cards.