Think again:
Fragmentation: when the developer needs to support obsolete os shiping with 'new' phones.
Progress: when the devoper needs to update their apps for the latest os that ships with the latest phone.
iOS 6 will never be shipped again with any phone. No fragmentation zes moi.
Is the end result not the same? On Android, it is more work for developers to make sure new apps work on older devices and thus might result in less (quantity and quality) apps for Android.
With iOS in this situation, the app is disappearing from the app store. Apple is making it so devlopers have to do more work to make older apps work on new OS. Less apps for iOS but many people are just making excuses like "ive never used that app, so no big deal."
In both cases it is more work for the developer because of having to support more than 1 version of the OS. Stop trying to find technical reasons why it is different.