That's not really proof that you were doing things correctly. You could well have been relying on undocumented corner case behavior that just happened to be true in one version of iOS, but not the next.

Awhile back, a bunch of apps got updated with what the authors called "fixes for iOS5." I have an app on the store that works all the way back to iOS 3.0, and it needed no updates at all for iOS5.

Occasionally Apple does take away documented, working APIs, but it's rare. In general, I'd say an app needs updates for a new version of iOS mostly because the author assumed things that weren't true.