And yet Apple devices have longer software support lifetimes than any Android devices and better resale values for a longer time. That hardly sounds like a set of characteristics you'd associate with products designed to become obsolete.
They are dependent on Apple for updates due to the code signing. Alternative operating systems also cannot be installed once Apple stops supporting them. That ensures obsolensce in the long term, even if it is longer term than their competitors' blob-ridden Android products.
Anyway, plenty of machines sold then and even today are junk, so maybe replacing them is not such a terrible idea. However, I think replacing the software matters more. Linux is an excellent option for these systems in the long term. If Apple made Mac OS X available for them, it would be too.
Is Android the right comparison? Because I don't think Android when I think about my barely useful iPad 2 (because Android tablets are tire fires), I think of the Pentium III Thinkpad that I use for distraction-free writing. They're both about as useful to me, and one is as old as a high school sophomore.
Realistically the early iPhones and iPads were an experiment. Nobody really knew what their useful lifetime would be. The same went for Android devices.
In fact the wisely received wisdom was that Android devices would have longer useful lifespans because open source leads to higher quality software that's maintained and updated for longer, which can be customized by users so it meets their needs better. The reality that many Android devices never see a single software update and are junked up with carrier crapware and poor device drivers hidden in binary blobs still hasn't sunk home for everyone yet.
Even now when I buy a new device I think about how useful it will be and what it's support will be like for 2 to 4 years. Beyond that, there's no way to tell. When my kid's original iPad Minis get replaced, if they still work I'll probably just use them as family photo and video galleries.