As a user I like the pay-once model, but for apps that provide continuous upgrades, a subscription model would make much more sense and I think Apple & co would

As a user I like the pay-once model, but for apps that provide continuous upgrades, a subscription model would make much more sense and I think Apple & co would do well to start actively supporting that model for apps. The ultimate guitar tablature iPad application does it via an in-app payment and I'm more than happy to pay the yearly fee. I could imagine doing the same for many other apps. The counterpoint here is that, as a user, I would then feel entitled to frequent and substantive updates which would increase the load on an indie even more.