Ok so it took me ages to realise that the odd tweet-counter-looking thing was a link to the comments. Enough with the secret sauce, guys!
The phasing issue the first illustration highlights is uniquely american. It's extremely rare for a domestic supply to have two phases and a neutral to the breaker box. You will see blocks of flats and apartments getting two phases but the individual breaker boxes all have a single phase. Even a lot of commercial isntallations will only have one phase.
Am I the only one that thinks using the CPC as a signalling wire is asking for serious trouble? The whole point of protective conductor is that it only carries current if you have a fault condition in order protect the installation and facilitate ending that fault condition. Quite apart from the possibility of tripping breakers for "no reason", sending signals down the CPC is deliberately introducing a fault current into all the exposed metalwork in the entire installation. A system like that will kill people sooner or later. I don't care if they're saying there's some limit on the current - it only takes one overcurrent at the right time.
And of course the liability for that falls not on the owner, or even the person who sold them the plug, but on whoever installed and inspected the installation.