Our CIO did an information session about a year ago. He made one interesting comment. He said that in WORLD CLASS IT organizations, 25% of their computer systems (hardware/software) were obsolete! An organization of any significant size just can't afford to keep everything current, especially when what you have is running without issue. And given the steady stream of industry stories about upgrades gone bad, is it any wonder organizations will just leave well enough alone and deal with it when it breaks? I don't think so.
The best thing to do if you have these types of systems under your care is (1) warn management about the risks involved and (2) have a contingency plan for when it does break. Of course, when it does break, that won't necessarily stop them from wanting it fixed immediately or placing blame off of themselves (with good managers it should but how many of those are there?).