Users of older iOS and MacOS devices, are now starting to feel the pain of Apple's platforms fragmentation. Experiencing Apps puchase attempts that instead result in a notice, the app is not compatible with their generation of device. Apple now has to try to retain those customers. In many cases I see my associates, friends and family decide to try a different platform. Often they are happy. They still use the old Apple device, but they don't buy apps or content for those any more.
I look forward to Apple's responses and attempts to stay relevant. They've been successful in the past, and I'd like to see them remain successful in making products I and millions of others will purchase and enjoy.
If fragmentation means that your device is no longer supported with new apps, then that is a function of the difference in market size between the older generations and the newer, and the fact that few people buy apps past an initial phase of ownership. This isn't even in the same ballpark as Android OS, manufacturer and device variations, so in fact, Apple is doing a superb job.
The screen has gone through three major iterations, and each has backward compatibility with previous generation apps. The glitch is that hardware in newer devices has capabilities not available in older generations. Developers create products for the newer hardware capabilities, and now the 4 inch retina display. That's where the buyers are. Generally, if you have an iPhone 3GS, or an iPod Touch 3 or newer device, you shouldn't be all that limited on apps.
I have an iPod Touch ist generation, and a friend still uses her original iPhone. Good enough technology for its original purpose, but there is little in the way of new apps available. I expected that and should a particularly enticing app show, I can always upgrade to new hardware.
Many people pass down their older Apple iOS devices to their kids, extended family or friends, and others sell them.
Fragmentation as you call it isn't that much trouble to deal with, and frankly, even Android OS device owners seem to have made peace with the fragmentation that they encounter.
It's just not that big of a deal for iOS or Android OS, and while I expect better and longer support from an Apple device, I don't expect lifetime support.