I'm not quite sure what you mean by "state-of-the-art", but I think you're over-representing Apple's relative quality. I've used various versions of OS X for significant amounts of time, but I've never seen what makes them so much better than everybody else. Gnome and KDE aren't perfect, but Apple isn't any better. (Seriously, I can't have a full-screen program on one monitor and normal programs on another, and that's the state of the art? I hope not.)
On top of that, I've found that most of the problems with KDE (I haven't actually used Gnome much) have been consistently eliminated in newer versions. When I started using KDE around 4.4, I was annoyed by several little details. Somehow, even without any input from me (I'm really lazy), almost all of these little issues were fixed in subsequent versions.
For example, the GTk build of Emacs can only be resized to the nearest character--you cannot have a window that overlaps has half a character off screen in either direction. This actually makes sense for Emacs; certain normal commands and interface elements would not work properly if you could resize that way. Normally, this is not a problem; however, if you used KDE's fullscreen shortcut, it would properly hide the borders and maximize Emacs, but it would leave a strip of desktop visible because Emacs can only be sized to the nearest character. This was a little annoying, but certainly not a horrible problem, and yet it was actually fixed shortly after I found it. Now fullscreen mode fills in any stripes like that with the correct background color, even taking things like transparency into account.
Over all, KDE is still the best desktop environment I've used anywhere. Given the relatively smaller amount of resources behind the project, I'm very impressed.
On top of that, I've found that most of the problems with KDE (I haven't actually used Gnome much) have been consistently eliminated in newer versions. When I started using KDE around 4.4, I was annoyed by several little details. Somehow, even without any input from me (I'm really lazy), almost all of these little issues were fixed in subsequent versions.
For example, the GTk build of Emacs can only be resized to the nearest character--you cannot have a window that overlaps has half a character off screen in either direction. This actually makes sense for Emacs; certain normal commands and interface elements would not work properly if you could resize that way. Normally, this is not a problem; however, if you used KDE's fullscreen shortcut, it would properly hide the borders and maximize Emacs, but it would leave a strip of desktop visible because Emacs can only be sized to the nearest character. This was a little annoying, but certainly not a horrible problem, and yet it was actually fixed shortly after I found it. Now fullscreen mode fills in any stripes like that with the correct background color, even taking things like transparency into account.
Over all, KDE is still the best desktop environment I've used anywhere. Given the relatively smaller amount of resources behind the project, I'm very impressed.