So far out of date?
Honestly, there isn't a whole lot of movement in phone hardware. Especially now that is has, for all intents and purposes, plateaued. Sure, there are the users who want the latest and greatest phone just because its manufactured date is newer than their old phone, but the majority don't want to upgrade until the additions are useful or their device is performing very poorly. I'd argue that the biggest limits to the majority of users phone lifespan is the wear on the battery and the wear on the NAND. Especially since Android didn't get TRIM support until 4.3.
I'll ask you a counter of your question... What features have been added to Android phones in the last year that are must haves?
And I ask this as a frequent early adopter... My older handsets usually end up in my wife's hands so I do care about updates lasting more than a year...
I can agree with this. I honestly don't understand why OEMs can't offer a standard upgrade time frame like this. Outside of everyone's desire to make you upgrade sooner...
Well, I just mean, if you are the kind of person who NEEDS every update, and ASAP, you probably are the kind of person who wants the newest phone as well, no? I honestly don't think that phone hardware has hit that plateau that desktop systems have yet. We're still adding features and massive speed, which is allowing us to use more and more complex apps on our phones. Each year's new CPUs are greatly faster than the previous. I think there's a lot left before we really reach the hardware plateau.
That said, we've definitely started to get there. For those who aren't phone nerds, most phones are plenty adequate today. Look at the Moto X. It's a step back on specs, but it's my go to suggestion for family and friends because it still runs great even if it's not cutting edge. We may not quite be at the plateau yet, but we're certainly getting closer.
For me, a lot of the drive to update is in displays. A bigger and better display has kept me upgrading. Now we have 1080p as basically a standard on phones. CPUs have gotten ridiculously faster, compare the Snapdragon S4 to the Snapdragon 800. Increased memory has been useful for taking advantage of newer OS features or bigger apps, and overall phone design (I jumped on the N5 because I'd been waiting and complaining for years for someone to make a phone with only onscreen buttons, next I'll be looking for an edge to edge screen). Cameras obviously improve, if that matters to you. If you're asking how the hardware has changed, if you care enough or want/need the features, a LOT has changed in the last year or so. If you just need a simple phone to make calls and texts on and play a few games or apps now and then, then probably the One X would still be fine, but you'd probably also be fine with 4.2 as well.
To counter your counter, what software updates have been added to Android in the last year that are must haves? The last few versions of Android, while certainly adding some new features, have been a lot more about polish. The last must have feature for me was Google Now, I believe. Of course, when you're a phone nerd like me, every feature is a must have feature, but I could use 4.2 or probably even 4.1 and have no complaints for the most part. Hell, I was just fixing my friend's Optimus G Pro. That's still on 4.1.2. Certainly new features have been added, but I'd say hardware has evolved far more than software in the last year or two for Android, which is why I say that if you need the latest software so badly, you probably are the kind of person who wants a new phone as well. I understand the cost factor of a new phone though, whereas software is free (to you, obviously not to the company putting man hours in or it wouldn't even be a discussion). To those people I say take a trip to XDA.