I ever cared for Gnome; lack of easy menu hacking and navigation and not being able to set different backgrounds for each desktop were among my peeves.
KDE4 didn't work for me, either. Too much slickness for stuff I had no use for.
Lucky for me some smart, motivated people decided to keep KDE3 alive. My eternal thanks to them.
A downside is that most often when I search for help on something it ends up being how-to in Gnome or maybe KDE4, but with a bi of digging I find what command line invocation to run or what config file needs editing.
Truly a great thing to be able to have such a range of UI options (and every so often I try xmonad) while under the hood it's same hackable OS.
But the really nice thing is I can always toss on a new WM or whatever and try it out with very little trouble.
IMHO the complexity gets a bit too high, and cost of maintaining forks gets too big, so even free licensing does not really matter anymore. One has to be very motivated, to keep up with his fork.
Having lots of choice for window managers is decades old and completely normal. It's modular and it continues to get easier. I don't see any burden but perhaps I misunderstand.
I just have a feeling (highly subjective, sorry) that some major GNU/Linux distros (especially Ubuntu) are turning from a distribution of loose coupled exchangeable components to monolithic tightly-integrated products.
Well, Debian seems perfectly fine in this regard, so even as Ubuntu user (for now) I don't care much about the situation. Sorry - I were wrong writing like this was about the whole GNU/Linux ecosystem.
(Edit: I should clarify that I'm writing this in anticipations that the general sentiment will be that Unity is terrible. If you don't think it's terrible, then it's also not an issue.)