A new survey from mobile operator Vodafone UK has claimed that people are now keeping their mobile devices for longer, with the majority upgrading every 4 years
I could understand upgrading so frequently at the advent of mainstream smartphones, where two years of progress actually did represent a significant user experience improvement - but the intergenerational improvements for most people's day-to-day use have been marginal for quite some time now.
Once you've got web browsers and website-equivalent mobile apps performing well, software keyboards which keep up with your typing, high-definition video playback working without dropped frames, graphics processing sufficient to render whatever your game of choice is for the train journey to work, batteries which last a day of moderate to intense use, and screen resolutions so high that you can't differentiate the pixels even by pressing your eyeball to the glass - that covers most people's media consumption for the form factor, and there's not much else to offer after that.
If the batteries were easily replaceable, and the software didn't continually get bloated, and companies kept issuing security patches, sure.
I kept my last desktop system for 10 years. Actually I still have it and it performs sort of ok (I was running Mint the whole time). But I upgraded and the performance improvement was actually worth the considerable cost. I've gotten similar life out of my other desktops and laptops over the years.
I think at least 5 years or preferably 10 is reasonable for smart phones.