it's not VSS that's the difference.  it's that no matter what you're using, you get a hard, unrealistic line.  fine for toons, not fine for anything else.  material zone edges don't blur, and i can't think of one situation where a hard edge around the lips would be realistic.  hard edges on other places, i could see working for second skins.  but in what situation would a hard edge at the lips be realistic?