So here is an example. Universe has all system and user-mode emulators for QEMU, it's 20-odd packages. To what extent will Canonical fix bugs in there, even for very old emulated machines? You don't know, but you know that they have no contributions upstream and it's one of the largest packages they have, so your chances aren't great.
Red Hat only has the KVM-enabled binary because, as the #2 contributor to the upstream project, they know exactly what can and cannot be supported. It also has dozens people of employed just to test it. If you have an issue it may languish because no one is perfect, but your prior is a little better.
