We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember John MacLeod
saying something like:

They probably had a good deal on 12v supplies -- the 5v regulator
inside would cost only a few pence, whereas they could save a lot by
ordering tens of thousands of 12v supplies rather than a more limited
number of 12v and 5v and who knows what else in between. Makes sense
to standardise on the highest voltage required by any of the line of
items which might require a smallish power supply.

That happened with a PC radio receiver I bought years ago. The supplied
wall wart put out regulated 18V, but it turned out the receiver was much
happier with a regulated 12V (hardly surprising, as it was designed to
run off a car supply for portable use with a lappy). On 12V it's much
cooler, as the internal regulator isn't doing much work.