[Dylan16807]

Your quote omits the critical "that only talk to hardware and not the internet". Your examples 3 and 4 are doing it wrong.

Stuxnet-like attacks can go after non-networked equipment, but they're based on exploiting the computer with the programming suite, not the industrial system itself.

[anglebracket]

That's fair. My point was that in reality, a ton of people end up doing it wrong in some way or another. You should cover your bases and keep your systems up to date with security patches regardless of how segregated you believe they are.