I hope you are not referring to Apple, because compared to other companies , iPhones and iPads are the one who can run current software on older devices with almost no issues. Samsung and other android manufacturers on the other hand have not supported older devices at all until recently (and even now not as good as Apple does). My first gen iPad still runs perfectly fine
I think the Android world is worse, mind you - but old iOS devices are still left to rot. My 2.5 year old Google TV box being abandoned by Google (can't even log into the app store) was infuriating.
Well, 5 years time in the mobile/tablet space is like 20 years time in the PC space. Consider the changes in capabilities, cpu and gpu power, etc.
In that sense, it makes sense that most NEW apps are not released for the older versions -- how many apps are released for Windows 98 today?
Sure, it's "only been 5 years" but then again that's related to the technology space. E.g. most would accept that a 20 old year PC/OS wouldn't get much support, but that would sound too soon in other industries, where even a 50 year product can still be supported.
Besides, as you say, this is much better than the Android situation -- since most devices are sold with an OLDER than the latest version, and most vendors don't care to provide updates for older devices.
It still works fine, but it's hardly because Apple are doing me any favours (past building a good product back in 2010, and "supporting it" with OS updates until 2013...)
iOS 5 smooth 60 FPS responsive interface, compared to 9 stutter fest. What added value does the iOS 9 bring to the table then ? The content in Facebook, Instagram, Youtube etc. is all the same.
But backward compatibility does not preclude Apple from being an upgrade company. Apple may not have invented the hardware upgrade cycle, but they've mastered it. That's what their keynotes and media interactions are all focused on. Their employees go out of their way to check if you have an "upgrade" available. I've had a phone that has never been in contract and they even offer to use that line to give me a "free" upgrade to my main line. I could go on... But the point is, the upgrade cycle is what Apple is all about.
Then there is the problem where it doesn't rotate properly. And my first instinct would be to blame the hardware, but in the case of Messenger, it rotates some parts of the screen and not others. But the parts that don't rotate are unresponsive. So I'll sometimes find myself in a situation where I've typed a text, and the message is rotated, but the text box and send button are not, and pressing the send button does nothing until I manage to get the entire thing to rotate by moving it from landscape to portrait and back a few times.
It's also possible there is some cruft I've carried over from previous version (I've upgrade a few times) so I'm going to try a 'fresh' install where I lose all my data and have to redo everything by hand and see if it fixes the problems. But the only problem I had prior to installing iOS 9 was my music not transfering properly, and AFAICT, that is an iTunes problem relating to duplicate tracks that I haven't had time to resolve yet.
If it's not the cruft, I guess I take it back and get a "new" one; maybe a problem with the RAM?
Full disclosure: have a Z3, mostly for this and because it was waterproof. The screen is now partially detached in the top after less than one year of use which annoys me but I hope to get it resolved under warranty.
android auto does not work on the z3 compacts at all because of their decision to remove the USB charge mode from the phones.
Also: anything else they have disabled?
See difference between iOS 8 and 9, who introduced stuttering in two and one year old devices.