Also if you look at the open source desktop's history, KDE was started before GNOME. GTK and GNOME was actually started because of the free software guys' concers that Qt was not free software, it just had a "gratis edtion", so GNOME was actually born to be a duplication, and in the end it ended up being good for KDE that GNOME was being developed because Trolltech was kind enough to release Qt under the GPL, so in the ended, the process of developing GTK and GNOME actually "liberated" Qt (I'm in RMS mode here).
'Ey Dann if you read this, I hope the above makes sense.
Also another thing I like about having both a GNOME and KDE app for doing the same thing is then you don't have to have both Qt and GTK libraries loaded into memory and thereby saving some resources, for example, right now I use CastPodder, which is a GTK app, for receiving podcasts (I could use BashPodder, but I like an app that I can sort with and stuff like that) and it's typically a little slower than the other Qt/KDE apps I run.
And finally as Zack also mentions, choices are not bad, and competition are certainly not bad. Why is it that Microsoft's products and support are so bad? It's because they run a big monopoly and always kill their competition using the courts and lobbying instead of actually making a better product and now that strategy is biting them in the ass.
I always think that "Free software and open source enables competition", for example Red Hat and Novell may be a little cranky at each other over the whole XGL/AIGLX /accelerated X subject, but in general I see them as compeditors, not enemies. For example, I believe Red Hat ships Ximian's Connector plugin in some of their enterprise products if I remember correctly, that's good for the users in the end.

