« on: May 15, 2012, 02:58 PM »
Perhaps Vader is hoping Luke doesn't have the guidance to know that Vader is the one causing his friends pain. Remember, he is using them to lure Luke in, and of course he'd keep them alive until Luke is in his clutches. What if he hears Luke is coming in, he kills the others rebels, and Luke decides to turn around and leave? Vader would have wasted a resource that was proven to have drawn Luke in. Vader doesn't know that Yoda is alive and is training Luke to be a Jedi. Maybe he assumes that Luke will just respond to his feelings. You don't pull away the bait until the fish is snared.
Also, once Vader has his moment with Luke on the gantry, he does not kill a single person after. He doesn't murder Piett after the Falcon escapes, he doesn't do anything to Jerjerrod, and they even cut out a scene where he attacks one of Palpatine's security officers. I think his confrontation with Luke changed him.