Well from the reports of penetration tests I've heard, many places do claim their systems are not connected to the internet, the gap has been bridged by someone, be it management or whomever. Someone above said he's heard of people bridging the networks with IR interfaces. When I interviewed computer security professionals at local power plants for me research on this topic, I was told people connect things to the network all the time that are supposed to be isolated. Even the government's classified network gets bridged to the internet from time to time, and there are strict regulations on the air gap for it. Maybe your companies actually maintained an air gap, but if your entire security method is compromised when someone accidentally plugs something into the wrong port on the wall, you've seriously failed in your duties for security. If you protect it like its on the internet, even when an accident happens and its plugged in you'll be protected.