Earlier quoted context omitted.
This can happen, when non-scrupulous devs 'deprecate' an older version of their app in favor of the 'new' version. e.g., you buy 'CoolApp' and in-app purchase features for it. But oh no, 'CoolApp2' has come out and 'CoolApp' is no longer updated for newer devices, so sorry. Otherwise, an app, and its in-app purchase set remain available via a user's iTunes account indefinitely as far as I can tell.
Why is it "non-scrupulous" for a dev to charge for a new version of piece of software? Are they suppose to update an app forever without further compensation?
I'm not expecting CoolApp to be forever supported. CoolApp works fine for my use case, so I planned on continually using CoolApp until it made sense for me to upgrade. But now that CoolApp2 is the only version available, I have to buy the newer version alongside my new device. If I turn on my old phone, I can still use CoolApp without skipping a beat. I think that's what the other commenter was getting at.