However, if the vendors on your alternate OS marketplace chose to go the same route as App Store providers, there's not much to gain. It's not so much about the OS, but about the ecosystem and the culture of this ecosystem, including online services. (As far as I do know, there's no reason why you couldn't support legacy iOS versions and hardware via the App Store. It's just not part of the predominant business model. The same is true for most commercial websites.)