Comment 11 for bug 219944

APT automatically ensures that all packages with Essential: yes are installed on a dist-upgrade. Other packages are not required to be installed. There are many types of systems, and APT cannot know which things you need for your system. For example, you do not need LVM on a system without LVM volumes.

If packages change, than this is a problem with those packages. For example, when transitioning from sysvinit to upstart, there must be sysvinit dummy packages depending on upstart, to ensure that the upgrade works using apt.

In summary: It's not APT's job to keep your system running.