10 is almost certainly high. However, the rate of innovation does seem to have slowed down. To the point that all of my other devices from 5 years ago still act like new. My phone? Meh.

What will really kill this is lack of user servicable batteries.

I agree. I am very happy with my Nexus 5 and I intend using it until the hardware gives up.

For context, 5 years ago people were still using the iPhone 4S, as the iPhone 5 wouldn't be announced for another 2 months.

And yet, most PCs built 10 years ago can still run most modern software that is written for modern PCs.

Demonstrating how much Microsoft bends over to maintain backwards compatibility. Something that for all their other flaws they should be applauded for.

You mean the APIs. But I wasn't talking about those, but rather the hardware - the only thing that you need there is ABI (or at least API) stability for drivers. So you can pull the same thing off with Linux, as well. Basically, modern desktop OSes can run on decade-old hardware, although they will have reduced functionality due to some missing features.

Okay, let's say 5 years. I'm still using my first generation Nexus 7, and it's still working fine.

There's no rocket science in maintenance support (eg security patches) for 10 years. That's the only thing that is necessary to keep the device usable.

All the apps on the app store will be written assuming more powerful devices with newer API versions.

That's not really comparable.. the ecosystem is mature now.

But sure I am going far with 10 years.. and phones would need serviceable batteries to last that long.

What ecosystem becomes mature after just 10 years? A hard drive 10 years after the first one was invented in 1956 looked like this[0]. Is that mature? Phones are mature compared to 10 years ago, but whatever they evolve to in the next 10 will dwarf them.

[0]: http://images.computerhistory.org/storageengine/1966_Ferrite...

The smartphone was invented long before the iPhone. This is 10 years after it went mainstream.

And in ten years that iPhone has not changed much, except that the CPU/GPU rapidly caught up to current standards. The only other dealbreaker toward using it today is 3G support, and that's a 9 year old feature. If the iPhone 3G had the same relative performance to 2008 desktops as the current iPhone has to 2017 desktops, it would probably still be viable.

Maybe 10 years is a bit too high, but we're talking about high end phones here. I'd be surprised if the actual hardware wasn't acceptable 7 years down the line.