Well, it’s possible to upgrade Mint the same way you upgrade any Debian-based distribution, including Ubuntu, and I’m sure it works pretty well. That’s not to say it’s a good idea to do so. First, few people are experienced enough to troubleshoot problems related to APT. Second, it takes more time and bandwidth to perform an APT upgrade than to download and install a new release (which 900MB ISO can contain between 3 and 5GB of compressed data). Third, when you install from a live system you get a unique opportunity to see the new release, to test the new kernel with your hardware and to make sure things work fine before you make the jump. Now with this said, things can certainly be improved. We should probably insist on people creating a /home partition during the installation, we should probably implement safeguards on UID and permission checks after a fresh upgrade… there’s definitely work to be done for upgrading to be made easier. Ubuntu’s recommended solution isn’t something we want to back though, it’s not good enough for us to recommend. Automation is one thing and making a process trivial is usually an improvement, but when that process is risky, automation is really dangerous.