"Principles" (I prefer that term to "rules", as it allows for the obvious existence of exceptions, and sounds less dogmatic) can still be handy as a guide, even if they may be of no interest to some and a red rag to others.
One thing I would be very interested to find out is whether the side defined by "principles" as the obverse is still the one actually produced by the lower die in the manufacturing process - this could be of importance to those who study die linkages, sequences of die cracks and degradations, etc. So is the Queen's effigy on UK and commonwealth coinage always on the fixed (lower) die, with the reverse on the moving (upper) die? Anyone know?
This question is directed to those who *do* care (and are prepared to discuss sensibly): in around 1946 - not sure of the exact date, would have to trawl through some Japanese references to find it again - Japan decreed that the sides known as the obverse and reverse were henceforth to be swapped. Anyone know why? Was it in fact a technical factor, e.g. putting what was the "obverse" die in the upper part of the striking machinery and vice versa, that gave rise to the change? That has always puzzled me, and I've never got around to asking about it before.