Reportedly, the bizzare "12 hours in the 2nd of the two years" bit came from the German delegate to JAA.
I've never heard of an explanation, but it is a stupid rule because basically what happens is that Joe Bloggs gets his new PPL, and realises he doesn't have to fly at all for 23+ months, so he doesn't bother with keeping current, and obviously after 23 months he will have forgotten what a plane looks like, so he packs it in.
6 hours per year would have made far more sense.
Of course 6hrs/year is not enough, because even taking it most charitably in currency terms (flying 30 mins every month i.e. 10 mins taxi, 15 mins airborne, 5 mins taxi) is no good.
I suspect there are many pilots who do have very poor currency. I am sure most of them know it and they stick to very simple flights. Or maybe some fly as passengers, which they can't log but it is still very good for them. Cost sharing is a big thing on the PPL scene.