Ah, Ken, Ken, Ken. I'm not as stupid as you (and others) may think!
It is not normal if there is HIGH pressure in the system when cold. A little pressure is no big deal, and could even be called normal. 15+ psi is way wrong when cold, period. I don't know why you think American/Japanese cooling systems aubmit to different laws of physics than German (European?) cars do. Try the simple squeeze test on the upper radiator hose with the engine cold. If it can be "twanged" like a guitar string that's not right. It should be soft & squishy. The cars never did this before, so do you mean to imply that zero pressure when cold indicated a *problem* with my cars, when they were running perfectly?
I don't think "engatawork" necessarily has a problem, though - it depends on the amount of pressure being described. I say that because he has an OM617, which are MUCH less prone to this type of failure. The OM603's have a known issue with head gaskets and cracking, 617's don't. I do think it's odd that the liquid in the tank was cool with a hot engine, sounds like possible flow issues? Thermostat? The level not changing doesn't surprise me, it usually won't unless the coolant is quite hot. But, as you say, if there is no coolant loss or overheating it might not be worth investigating.
Remember: Both of my 1987 OM603-engined 300D's, with high pressure when cold, ARE LOSING COOLANT!! Quite rapidly, too - a quart per 400-800 miles.