I think the point is that a standard network is generally the wrong thing for control - therefore you would not want to hook up standard car navigation/media player devices to your control network, but non standard ones which "get out of the way" when necessary. Ethernet (despite all it's nice features) is really unsuitable for control. I know - I've played around with remote IO on ethernet. Devicenet (aka CANBUS for industry) beats the pants off it in terms of latency at lower baud rates on all but dedicated networks. Wrong tool for the job really.