Interesting!
Of course, the interconnection of all those bathroom elements, properly termed "Earthed Equipotential Bonding" also results in their being grounded to earth. The process of bonding aims at achieving equal potential, as MRX states...but as soon as a connection to earth is present, everything is, obviously, also grounded.
One may occasionally still find a 25Amp 230V Single Phase setup in Munich,(stoves/cookers for instance can still be wired for that) but generally speaking, we use three phase for any single consumer taking more than a 16 Amp Single Phase circuit can comfortably handle. The instant water heater for my bathtup/shower for instance or a large motor - three phase motors are cheaper, more reliable and easier to build.
Before the Europeans get all too excited about American electrical system deficiencies, my apartment was still earthed using TN-C, or "classic bridge" - earth and neutral were the same conductor when I got it. I made such a scene that the entire system was updated, but it left me with a very bad taste in my mouth regarding wiring elsewhere in the house...it only takes one in-duh-vi-dual to reverse P/N and things can get very interesting.
I have to agree, the Schuko outlets seem to attract and hold dirt, grease and grime. The only sensible way to clean them is to unscrew the outlet cover and run them through the dishwasher. At least I've never found a better solution.
Question: Was the old "two hot wire" system in the Netherlands split-phase or two-phase?