For TOR I can agree with, with KOTOR less so. In KOTOR there are characters that will acknowledge your change of appearance, and within the context of the story the Jedi were pretty much forced to rely on Revan and Bastilla to save the day, so even if you were slipping to the Dark Side, I think all they could do is simply let you carry out your mission and pray for the best. Whereas in TOR, yeah it makes less sense because you should be more expendable. But I'm not even talking about simply player characters. NPC Sith show great variety in appearance. NPC Jedi are all pretty much just normal, but the Sith can range from normal to monstrous.