They're plentyful in my area as well, mainly inside GE M250A2 fixtures. It's probably the 3rd most common wattage, 100W HPS being the first, then 400W, and 200W very close behind.
My area for my electrical company smaller fixtures are 100, 150 watt HPS and for the Medium sized fixtures (usually GE M-400A3s) are 250 watt and 400 watt HPS and finally 1000 watt HPS used in AEL Model 327s!
OVX is sorta in the small catagory....the OV-400 was simply an OV-15 with 400 watt ballast, same for the L-150s which had a 400 watt support, and so did the OVS which could handle 400 watt and now the OVX.....
Yeah. They should stop doing that. There's no point in even having a medium size fixture if they're going to do that. Using 400w lamps in small fixtures is like trying to kill the lamp! Especially in Cooper lights because of the reflector thing although it mosly occurs with HPS.
Its actually not a problem witb 400 watt MV.....its only a provblem with 400 watt HPS....it was actually started by the 400 watt MV...not the 400 watt HPS