What you say used to be true, but does not appear to be any longer.
When was the last time we had useful improvements to the OS X user interface? 10.4 (2005) or 10.5 (2007), in my opinion. They've certainly improved under the hood, but the improvements to the UI have been mostly gimmicks like Expose.
When was the last time we had useful improvements to the Windows UI? That would be Windows Vista, 2006/2007. (W7 was basically just a stable version of Vista). Windows is certainly attempting to add improve the UI with Metro, so it's a 5 year timeframe to wait for improvements.
OTOH, in Linux land we've had KDE4, Gnome3 and Unity all land in that time period. Every 6 months we receive useful new improvements to our UI. Sure, the initial reception to KDE4, Gnome3 and Unity were all negative, but the haters are always the loudest. I haven't tried Gnome 3, but Unity 12.04 and KDE 4.8 are both really nice, much better than the OS X or Windows 7 UIs, in my opinion.
And it's not just the UI. It takes about 10 seconds for my computer to leave the BIOS and have both Firefox & Emacs open in Ubuntu. It takes the same machine over a minute to have Steam open in Windows.
There's just one problem with your post: you're thinking like a technologist, and not like an end-user.
End-users don't want to have to learn an entirely new UI (read, a different way of doing things; or, "Where's my Start button? Everything I know how to do is under that.") every couple of years. Not because they're (all) dumb, stupid, or lazy.
It's because end-users view a computer as a tool to do what they need/want to do--quickly and efficiently. Anything that distracts from that (like having to re-learn where everything is, and how to do the task they've
done the same way for several years) is a negative and annoyance.
Unfortunately, the technology community has forgotten that.
Which is one reason why the 6 month model that the Linux community has adopted is so great. Every 6 months Unity or Gnome3 or KDE4 incorporate some improvements, but the differences are not major and are easy to learn or ignore. But over time these differences accumulate and become significant real improvements. We get to have our cake and eat it too.
And hopefully these environments have learned their lessons now and haven't incurred the large technical and design debt that necessitate large breaking changes. KDE is up to 4.8 now but nobody is talking about a massive rewrite for KDE5 -- it's just another incremental update. OS X appears to be moving towards this sort of model too, with fairly regular yearly updates. Windows is the only one bucking this trend with its major upcoming breaking change in "Metro". And they're getting pummelled for it.
There's just one problem with your post: you're thinking like a technologist, and not like an end-user.
Well, a lot of people who use and hack on Linux distros aren't targeting the "end-user," they're targeting the technologist. So that mindset is not necessarily a problem.
If we're going in that direction, then everyone's participating in a different conversation. The original conversation was not whether or not this is a non-problem because end-users have issues. The original conversation was why hasn't Linux been adopted by end-users at the same rate as other OS's, if it's superior in so many ways.
Is funny, cos in the games industry the concept is that the average end users are completely willing to learn a completely new UI for each and every game, as long as it is fun.
You can't have a consistent button layout across all games though, as there is far too wide a variety of different functions to be mapped to.
Also, by having the attitude that the user is willing to invest time learning how to use the game, there is far more experimentation in interface styles being done.
When was the last time we had useful improvements to the OS X user interface? 10.4 (2005) or 10.5 (2007), in my opinion. They've certainly improved under the hood, but the improvements to the UI have been mostly gimmicks like Expose.
When was the last time we had useful improvements to the Windows UI? That would be Windows Vista, 2006/2007. (W7 was basically just a stable version of Vista). Windows is certainly attempting to add improve the UI with Metro, so it's a 5 year timeframe to wait for improvements.
OTOH, in Linux land we've had KDE4, Gnome3 and Unity all land in that time period. Every 6 months we receive useful new improvements to our UI. Sure, the initial reception to KDE4, Gnome3 and Unity were all negative, but the haters are always the loudest. I haven't tried Gnome 3, but Unity 12.04 and KDE 4.8 are both really nice, much better than the OS X or Windows 7 UIs, in my opinion.
And it's not just the UI. It takes about 10 seconds for my computer to leave the BIOS and have both Firefox & Emacs open in Ubuntu. It takes the same machine over a minute to have Steam open in Windows.