Yeah, I agree with canofhumdingers's interpretation of the scene. It makes Vader willfully evil to follow the Emperor. It just doesn't make any logistical sense to follow him for an entire generation if all he's really doing is waiting for a chance to overthrow him because he doesn't like what he's done with his life. If he was that unhappy with his decisions, he should have abandoned the Empire or simply killed himself.

And the new scene makes no sense because, as others have pointed out, Vader knew about Luke. He made it no secret that he knew about Luke. The Emperor wasn't calling up Vader to say, "Oh, yeah, by the way, your son is alive." That's common knowledge. Vader wasn't exactly discrete about this information, so it seems unlikely he was trying to keep his search for Skywalker a secret. The point of the call was to inform Vader of the increasing threat. Yeah, Luke destroyed the Death Star. Yeah, he's a key figure in the Rebellion. The Empire needs to get its revenge against him. But now Luke is becoming stronger in the Force. That's the great disturbance. He is becoming a threat, not just to the Empire at large, but to them personally, and to the Sith. He was about to get additional training. That's the purpose of the call. Not to establish family ties or to waste time with some very obvious (to them) family connection. That's just a silly way to (re)interpret the scene, and it's obvious George wasn't thinking too hard when he re-wrote the dialogue, otherwise he would have realized that it doesn't make sense.