I for one don't want to fight against the subdivider/smoother while trying to make subtle morphs to a low-res model.  Sub-D at render time I wouldn't even be able to see what I was actually doing, it would have to show up in the preview window too. 

You need vertices to morph, and you need them dense to morph with detail.

(On the other hand, on Genesis, my old V4 morph looks exactly the same so I guess it can work out okay, I just don't know how it's doing it.)