Its very common to have only one, despite it seeming cheapskate it does have one important benefit.

Most makers manage to cram all the lights, front and rear into a single cluster, if you have two rear fog lights they diminish the sudden appearance of normal bulb equipped stop lights, by only being on one side hopefully the NS stop light is more noticeable...obviously this isn't quite such an issue with vehicles equipped with high level brake lights.

One reversing light i do have a problem with on larger vehicles like 4x4's, fortunately the bay of E is a handy source of some rather juicy LED replacements that can up the output from that single candlelight to around twice what two 21w bulbs could provide.

Whilst i'm on a rant about lights, with these fashionable front light units all mirrored reflective and wrapping half way down to the wing, have you noticed how the indicators in particular are almost impossible to see in sunlight, and not much better when DRL fairy lights and headlights are on as well, normally i would cite VW's efforts here, but t'other day i nearly pulled out on a roundabout on a new Corsa, wasn't till it came full on view looking straight at me that i realised he was indeed indicating right but for all the use the indicators were he needn't have bothered.

Bring back Subaru and older Toyota LC's who fitted solo indicator lamps a good hands distance from the headlights and with unfashionable orange lenses, you could see them flashing whatever the light.

I am a great fan of symmetrical rear lighting and cannot fathom for the life of me why manufacturers mess around with dummy red or white lenses to camouflage their penny pinching. Why can't we have a universal standard of TWO reversing lights - one each side - for maximum visibility and ONE central foglight?