comments like this...
"Even the idea that any decent sized firm has a plausible list of all the systems they rely upon was met with a mixture of laughter and scorn."
Bullshit. This just means that you aren't employing the right people, or if you are, they are overworked. Any network administrator worth their salt can tell you every device on the network, when they're used, where they connect, and what's running there. For example, if your developers start running production code in their lab, your network administrators should know about it, ...AND... have the power to get it relocated to a proper system and location.