Searching for a solution to a slightly different problem I found the site...
...with the following reason for Mint's update method...
"Why doesn't Linux Mint upgrade the way Ubuntu does?
"From our point of view, Ubuntu does three things wrong:
"1. It doesn't make it easy for you to backup your data, nor does it warn you to do so.
"2. It automatically asks you to upgrade to the latest version. You click on the "upgrade" button and there's no turning back. No explanation about the risks involved, no explanation about the pros and cons... just a simple button to click for a process you likely don't understand.
"3. It uses a "package" upgrade method. See section C2 for pros and cons associated with this method.
"The only advantage Ubuntu offers is that it makes the process trivial and fully automated. Though, considering the risks and the way it upgrades your system, this should be considered dangerous. We do not even recommend this on the command line, so to have it triggered from the click of a button is just not acceptable to us. It's easy alright, but it's not the right solution. Sometimes things are important enough for us to take the time to do them properly. When it comes to upgrading, it's important to backup your data, to test the release before installing it and to avoid any broken or conflicting packages. The method chosen by Ubuntu is fully graphical and extremely easy to use, but it fails to do just that, and that's what matters the most."
The site gives what appears to be a comprehensive guide to upgrading Mint. The page seems to have been written for Mint 9 (why do people never date their articles!?) but it seems sound for Mint 15 and others.