Those aren't the same, though. You can pay for a subscription with the App Store, and you can buy in-app "tokens" for games. But the subscriptions are being charged when they turn over each month (Apple will bundle charges together that occur on the same day, but that's it, AFAIK), and you can't exchange tokens back for cash. So Apple is never "holding" your money.
I was thinking more along the lines of buying iTunes cards to load money onto your "account", which you can then later use to purchase digital goods, at which point the funds are disbursed to the content creators, minus Apple's rake.
How is that different from putting money into a Patreon account, which can later be allocated to content creators, at which point the funds are disbursed, minus Patreon's rake?
Ah, I see. But I think that's still the same "one-way conversion" thing that avoids the issue, right? If you buy a $50 iTunes card, you can't spend $25 of it on iTunes and get the other $25 back as cash.
Patreon could certainly do that, but either they haven't considered it or--probably more likely--they don't like the idea. There could be practical reasons for not wanting to do that; a lot of people have talked about Patreon's problems with chargebacks, for instance, when people want to cancel pledges but they're bundled together with pledges they want to keep going all in one credit card transaction. In this balance card scenario, it'd be easy to have someone say, "Hey, I wanna cancel the monthly pledges I'm giving and get my balance back," and they could lose a lot of goodwill if they say, "Yeah, you can't do that." (While many of us would rather receive cash than gift cards, we generally understand that an iTunes gift card is something we can only use by spending at iTunes.)