LFAJ,
I'd say you've got it about right, despite the wine!
As far as RPS in UK is concerned, my understanding is that in years gone by, when local QNH could be quite difficult to come by, it was a way of obtaining a "safe" (i.e. pessimistic) altimeter setting for a long flight out of radio contact. Some aircraft radios had only a limited number of frequencies and needed physical crystal changes by the ground crew in order to obtain others (I trained on some military aircraft that were like this).
These days, if speaking to an ATC unit close by, I always set their QNH, rather than RPS, so that the relative altitude of other traffic can be readily understood. One exception might be where I might have no-one close by to give me a local setting and so use London or Scottish Information, who can always give the RPS.