So how many Slashdotters really just stick with defaults no matter how much they like something else better? Seems like a total non-issue (and a non-complaint) to me.
The problem is that in most distros the default system is installed around the default desktop UI, so just typing
apt-get install xxx-desktop
might get you the desktop, but many apps designed for the new desktop UI only partially work, and some not at all. This is why kubuntu, xubuntu and lubuntu end up with their own install discs, even though (IIRC) they use the same repositories (ie, codebase) as ubuntu.