A financial product that is only available to iPhone users seems like a reasonable business, but if it's only available in one market it's limited and you can't build much else on top because it's slicing the market to granularly.
I realise that international financial products are hard, but isn't that the reason why Apple is delegating the finance part to Goldman Sachs (and I suppose, theoretically, others in other countries) – so that they don't need to deal with the nitty gritty in each region?