Earlier quoted context omitted.
> Mobile app stores killed that model, when they made continuous, perpetual updates the norm. Continuous, perpetual updates are definitely NOT the norm in mobile apps. Some get some bug-fixes and the occasional new feature, but any major update lands a version 2.0. Far more (the "long tail") are just abandoned (like all those thousands of 32-bit apps being deprecated in the iOS store).
Both apple and google don't support 'pay for upgrade' model. Its either subscription or pay once. Of course, you can roll out your own payment gateway(which apple has further issues with) or re upload the app under a new v2 name, but those are not very satisfactory solutions.
Not very satisfactory, but very prevalent.
And, I'd say, given the low price of apps, it might be just right to not offer any special discount for an upgrade. You could always reward older users some other way.