The real question here is; can the effects of a polarizing filter be duplicated in Photoshop, when shooting RAW? The darkening of a blue sky can certainly be duplicated in PS, but what about the reduction of shiny reflections from water and metallic surfaces? I haven't made any direct comparisons, but it seems to be a fact that an ACR conversion with a -4EC adjustment into ProPhoto RGB and 16 bit TIF (usually resulting in an extremely dark image) will retain the full tonality and detail of the RAW image. All that remains is to brighten the image, applying a tone curve or whatever, whilst retaining maximum highlight detail in those shiny, blown reflections.
I suspect the advantages of a polarizer, for someone au fait with most of photoshop's processing options, would be very slight.