I see where you're coming from, but perhaps a better way is to make it possible to offer discounts for a new app. E.g. Funky App 2 at half price, and to be able to notify users of the app at that new price.
The rationale behind this is that users can still be notified of major release versions without forcing them to upgrade or die (sometimes people continue to support older versions for a bit while the new version gets traction). For example, the new version of Coda when it came out was pretty buggy compared to the older more stable version and app store reviews showed it, but there's no way for people buying Coda 2 on the app store to upgrade to Coda 3 at an upgrade price when it comes out. Having the ability to provide a discount for not only Coda 3, but other Panic software at upgrade time could generate more sales for things like Transmit etc.
I'm not singling out Panic, just a recent example.
I like this approach - it doesn't break the existing experience of free upgrades.
While I can understand where the GP's idea of paid upgrades is coming from, the not-infrequent occurrence of apps going from Paid-->Free + IAP is often enough that I can see paid upgrades being yet another way App Store users get taken advantage of.
The rationale behind this is that users can still be notified of major release versions without forcing them to upgrade or die (sometimes people continue to support older versions for a bit while the new version gets traction). For example, the new version of Coda when it came out was pretty buggy compared to the older more stable version and app store reviews showed it, but there's no way for people buying Coda 2 on the app store to upgrade to Coda 3 at an upgrade price when it comes out. Having the ability to provide a discount for not only Coda 3, but other Panic software at upgrade time could generate more sales for things like Transmit etc.
I'm not singling out Panic, just a recent example.