IMO: 1.) Palps also had a warm laugh to Anakin in Episode II and III. He seemed really nice and sincere. But in reality he was a cold, ruthless, tactical Sith lord who used people for his own advantage. Palps wasn't actually nice in Ep VI. He was trying to convert Luke to the Dark Side by attempting to be nice. IMO I think it makes him look even more scary and creepy. 2.) His good side was NOT coming through. He was being sarcastic. Trying to tell Luke that he "really really truly cared about what happened to the Alliance." when he really was just trying to piss Luke off and make him realize the immensity of the situation. And try to unnerve Luke as well to make him join the Emperor.