Honestly people who buy new hardware every year are not "into hardware", they are into wasting their money and finding a pretense to justifying it. Most of them are probably just bored or treat it like fashion.
This is roughly what I observe. With the exception of a subset of techies, the people I know who always have the latest and greatest also tend to make very minimal use of the latest and greatest features. I'm not convinced many of them are upgrading for any purpose other than retail therapy.
A secondary hypothesis is that there is a contingent of people who buy and install smart home devices just to annoy their non-tech-inclined spouses. That one's not mine, though, I got it from one such spouse.
I think I can agree with this with regard to modern phones, but not universally.
For instance, in the early days on the iPhone, anyone who upgraded every year was getting a huge improvement each time. The iPhone 3G brought 3G support, so you could actually download things at a reasonable speed. The 3G S had a huge and very noticeable performance increase across the board, and the 4 was the first with a Retina screen.
Another example... for PC games, I really wish I could upgrade my GPU each gen. Especially when you're in charge of adjusting your own performance settings, the extra headroom you get from a new card always feels super nice. (Whether the increase is really all that noticeable is perhaps debatable, which I suppose would go to your point...)
