A lot of the ads used to be 'multi-national'. The car would have a number plate like 111 AVM. To change from RHD to LHD, they'd simply flip the film horizontally, so the plate became MVA 111 and the car would be on the correct side of the road for the intended country.
True, not many countries drive on the left, but I think Japan's quite a major market! I know what you mean though, we see the European makes on TV most of the time and they aren't interested in making a RHD commercial just for us!