Ubuntu inherits Debian policy. Anything--supported or not--is not updated in any way that breaks things. You might not be able to get security patches for stuff in Universe or Multiverse in a timely manner without rolling and submitting it yourself; but they won't go releasing a package that no longer does X when X worked before. The idea is that, if your configuration works, it will continue to work *exactly* the way you have it without modification no matter which version of the package you have across the entire lifecycle of a stable release--if it doesn't, that's a bug and they need to undo that breakage. Extending is fine, breaking is *not* acceptable.
I call bullshit. http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=561578#61