Oh I have worked with codebases (in large financial institutions and in engineering applications) that are meant to be contiguously maintained for more than a decade. They have been working nicely 16+ years and are easy to maintain with no downtime. Obviously, none of it involves the CLR or .Net. On the other hand, I've also seen seriously big projects ruined by .Net with no handover or documentation. But worst, no accountability. I've also seen a few successful ones but I would expect that culture to deliver continuous quality -- but it surely hasn't.

That's why I am saying that most of these claims people bandy around about enterprise computing are nonsense.