The first iPhone is as usable today as Windows XP is. The difference is that the features present in its successors (and the features NOT taken away) were enough to make the users upgrade (or, depending on your perspective, bad enough to make them jump ship).
This isn't me defending Apple or putting down Micrsoft. We might see this in the next few years with MacBooks or the iPhone as the perceived quality of OS X declines. My own wife won't let me buy her a new iPhone because she is happy with iOS 6.
Changing operating systems, especially in the PC world, is very disruptive to users. Especially non-savvy ones.
The hell I went through when my mom got a new PC with Windows 8.
I can't imagine Windows 10.
I guess a big OS is a different beast though as it's a billion dollar project in itself - I think at that point they just tweak a bunch of UI so people think they're getting something new.
Once you have the whole application, files and version of the OS it was running on in an emulator, you can practically run it anywhere.
Not so with things on the web :(
Take for example HRBlock - it has (or had?) a desktop version, and web version. I've used to desktop, but moved to the web, but makes me wonder - would I be able to review my data on it, 10 years ahead? Granted... I can pull all the data I need (after all taxes follow specific forms), but there are applications for which this is simply not possible.
Imagine if Photoshop/Maya/MotionBuilder/3DSMax/Word/Office were running exclusively on the web (and to some point some of these do). Now what happens in 20 years? Would someone be able to open the files I've created in them?
Yes, there would be someone... But that one would be the old desktop app, running under some VM, maybe under your new fancy watch/or whatever device - but you can still view it.
But not so about the web. If the application was purely done on the web, and even though you were able to export files/data from it, it comes to a point where you might not be able to show this data in much later years.
I still can run my favourite Apple ][, Oric, and protected mode (unreal mode!) DOS thanks for the fact that the application was all there, boxed, and if you've collected all patches ever released - you can relive it again!
Ahh... enough with the rant, you can't catch the web, it captures you :) lol
Screens change size, and pixel density is always increasing.
Input mechanisms change drastically too. 10 or 15 years ago, almost everything was mice. Now, there are more touchscreens than mice, and there are a hell of a lot of trackpads too.