> It doesn't need any sort of backend

It's far down the list as to why I decided to subscribe, but I do like the idea that if I lose my phone, my data won't be lost forever.

>This is exactly the sort of app that should have a single $10 purchase.

If you cloned the app and offered it as a one-time $10 charge, I'd be interested in that for sure!

> So why is there a subscription?

Recently they pushed out some updates that made the Watch experience a lot better. If you were the developer, would you have delivered that to $10 one-time purchasers for free, or would you have charged for a major version bump that had the feature?

> It's far down the list as to why I decided to subscribe, but I do like the idea that if I lose my phone, my data won't be lost forever.

You can pay for backup services with both google and apple. There's really no reason that data should be lost forever assuming the app stores data using that service. $7 a month gives you the ability to backup 1000s of apps worth of data.

> Recently they pushed out some updates that made the Watch experience a lot better. If you were the developer, would you have delivered that to $10 one-time purchasers for free, or would you have charged for a major version bump that had the feature?

This is a tricky thing. Sort of depends on where sales are currently at. I somewhat view this as the software not being complete before it was sold.

It'd be up to the dev if they wanted to run a new rev of pull out some good will to hopefully sell more apps. I'd assume you wouldn't make a new major version just for better watch integration. But then, there is the case of EA sports whose entire business model is releasing the same game with only roster and game player updates.