So,
How far back would you feel Apple should continue to support their older, legacy products?
On the computer side, Apple supports older Intel model Macs for up to 6-7 years! with OS upgrades/updates.
Older PowerMacs were supported, under OS X, for 6-7 years.
Computer technology doesn't move as fast as mobile device technology.
Mobile device technology becomes less powerful and obsoleted quicker with upgrades/updates.
4-5 years seems to be the cycle on Apple's mobile device support for iOS upgrades/updates.
Doesn't mean your mobile device is going to stop working?
It will still receive app updates for another year, maybe two!
So, if you hang onto your iDevice for another year or two, then the device was still effectively working for your needs for?...6 or 7 years!
Hardly "planned obsolescence" which the term, for me, at least, is much like a verbal malaprop or oxymoron!
A term started by technology users who can't cope with the fact that their new, current, expensive electronic computing devices are becoming slower, less convienient, less powerful and becoming obsolete faster than these users think it should.
How long do you think TV/monitor manufactures, DVD/Blu-Ray/ streaming media player manufactures, electronic, digital camera/video camera manufacturers, electronic musical instrument manufacturers should support all of their old, aging, legacy products?
This is a very subjective, rhetorical and circular argument.