alt Hacker NewsThe idea of a distro being "designed" around a particular DE has always annoyed me too. I'd hear people saying they wanted to try KDE so they wiped Ubuntu and installed Kubuntu instead and it's like, buddy you could have just... installed KDE. I know some specialized distros are really all about shipping a nicely-configured setup for their specific DE, but your old standbys like Debian, Redhat, Arch, Slackware, these are all infinitely flexible.
The idea, I think, is to provide a sense of GUI unity that Windows and Mac mostly provide. While it's nice in principle, the reality is you're going to install other software, and it's often going to use GUI libraries that don't perfectly match or match at all with your Linux DE. Personally, I've never found the need for a system to be designed so heavily around a DE. Like you said, it's entirely feasible and relatively straight forward to download Debian or whatever distribution and install a DE and chances are it will work ask expected. Well, until you perform an update/upgrade and boot to a black screen, but that's a different story. Once you've got your kernel and init system of choice, you can pretty much do anything you want. A premade DE is hardly even needed if you have a modest familiarity with how Linux works. The only downside is the added work from setting it up and debugging it, but people who use Ubuntu, Gnome, KDE, XFCE, MATE, LXDE, and so forth, end up doing that anyway eventually.