It's all about introducing more point & click, which some might see as evil
You could say that again EVIL "VERY EVIL"
I looked at that list. That's a personal sources.list of some person. Most of those sites bring in software that's not under the GNU license. Which is a personal choice. If a distro did that then they become respondsable for those Licenses.
Also with a sources.list like that, there is a good chance you'll get software that will brake your system. Your talking "point and click", most people that "depend' on point and click GUIs to manage their systems wouldn't know how to fix it after it was broken.
Actually Linux Mint does keep you pretty much up to date. It's the outside software such as skype that you need to edit your sources.list to install, or some multimedia packages. But after you've done that, your on your own, it's no longer a pure linuxmint system.