I just read on another forum that, "It's pretty much the standard nowadays to only have one rear fog lamp located on the drivers side. The reason given is that it's easier for following drivers to see the change in your cars rear lights when you step on the brake if you have only the one. Whilst that does make some sense you can't help feeling slightly short changed the first time you see it."
I also heard from my SA who said, "There is only one rear fog light. It is on the left hand side of the car so that following cars know where the center of the road is."
It's not odd at all -- it's been that way since rear fog lights were all but mandated by some European countries in the 1970s. The idea is to not mistake a rear fog light for brake lights, as well as what your SA said -- to give following traffic an idea of where road lanes are.
Not all manufacturers these days adhere to keeping the rear fog light to the left corner of the car. The EU-spec 370z, for instance, has it in the very center of the rear valance -- set low so that it's not mistaken for the third brake light. But rear fogs are, AFAIK, still single lamps.
Front fog lights and rear fog lights serve two different purposes. Front fogs allow you to see road markings, including reflective surfaces; their primary purpose is not
to make you more visible to oncoming traffic, though they do serve that function that way. Rear fogs are strictly for visibility, though: so traffic following your lead can see you and follow you.