If you've ever been in a position where you've bought an app only to have it retired from the iOS App Store and furthermore unsupported as a result of a new paid upgrade, you'll be happy to hear there is a workaround, though it doesn't seem to be a mechanism publicized by Apple. Basically, end users can find their old apps by navigating to the Purchased section of the app store - developers need only send this link to customers looking to download the old app again (with their own ID number, of course): http://itunes.apple.com/WebObjects/MZStore.woa/wa/viewSoftwareRedownload?id=295660203&mt=8&at=10l3Vy&ct=UUimUdUnU14840 . Developers can continue issuing bug fixes and updates to apps that have been removed from sale, so long as they don't delete the old version from iTunes Connect. It's a clunky workaround, and the download link is only accessible from the device, but it works.
Obviously Apple wants to give developers the power to fully and completely pull the plug on old apps, since it pushes end-users to pay for the latest and greatest. Plus if Apple needs to backpedal and remove offending apps that slipped through the approval process, they have a mechanism to do so. It's not such great news for end users though, since they paid good money for their apps, and to have them made inaccessible down the line is just pulling the rug out from under them.
Have you ever been put in a position where one of your older apps was removed from the App Store, never to be found again? Was a decent alternative available, or have older versions provided you with some function that didn't make it to future iterations?
Source: David Smith