I rarely spend money on the app store, but if I get a card I'll buy many more apps and games than I otherwise would have.

Kids don't have credit cards connected to their iTunes account, and thus receive iTunes gift cards for music, which they turn around and use for apps, IAPs for games, etc.

I don't have any source for that, or even necessarily believe it (I don't disbelieve it either) ... I'm just pointing out what OP meant by that comment.

iTunes cards are a hugely popular gift for children / teenagers / college kids, quickly exchanged for fart apps and in app smurfberries. The nascent Google simile of this is still minuscule in comparison, making gifting in the Android market a much less pleasant affair. I would gather that the KitKat promotion is partly to help spread awareness of Play cards.

As a second effect, people don't think of things like iTunes cards as real money. Give someone $50 on an iTunes cards and, I suspect, it will see much less discretion than a $50 bill.