I'm pretty sure it's the "can't take money back out" that's the deciding factor, yep. While I'm not positive, I think this is even true for (non-banking) government agencies -- I can load value on a transit card, but I can't take it back off as cash.
(Edited to add: of course, this means that Patreon could have done a balance card thing if they were willing to say "but you can't get your balance back if you cancel," but I doubt that would have won much more love than the per-transaction fee idea did...)
(Edited to add: of course, this means that Patreon could have done a balance card thing if they were willing to say "but you can't get your balance back if you cancel," but I doubt that would have won much more love than the per-transaction fee idea did...)