> Aside from host the infrastructure that delivers the apps
Under that logic they should charge for upgrades. But subscriptions is not really related to upgrades. Subscription implies that your app is tied to your own backend service that you keep up and running without Apple's help.
>> "Subscription implies that your app is tied to your own backend service that you keep up and running without Apple's help."
You could be using iCloud as your backend. You're definitely using their subscription billing infrastructure. You're getting access to their users credit cards without having to ask for them.
This is debatable. Recent changes and interviews with Shiller seem to imply that _any_ application can use the subscription model, even if it is only to pay for updates.
Under that logic they should charge for upgrades. But subscriptions is not really related to upgrades. Subscription implies that your app is tied to your own backend service that you keep up and running without Apple's help.