Of course, doing something as goofy as giving the installed system two completely different desktops and sets of software by default would have just spelled the death of Ubuntu, not just Kubuntu.
Too often the Linux crowd forgets the important of "polish," which among other things means not forcing the user to pick between two different ways of doing the same thing.
Whether KDE is better than GNOME is significantly less relevant in the grand scheme of things. Marketing and how the image is projected is significantly more important. "Here's the one thing we did and here's how freaking awesome it is and hot damn do you need to try this out" is significantly more powerful than "meh, do whatever you want, choice and stuff, we're open and that's neat and you should try one of the things we couldn't make up our own minds about."