I hate this line. I think the original dialog makes so much more sense. Especially when you consider the question often asked, “Why would they put Luke with the Larses if they were trying to hide him from Vader?” They weren’t.
This is how I like to figure it:
When Sidious told Vader that Vader had killed Padmé, it wasn’t part of a plan to keep him in the dark (no pun intended) about the existence of his offspring. It was just to cause him the greatest emotional pain possible, which completed his journey to the Dark Side.
The Queen of Naboo dying during childbirth is a difficult story to keep off the cover of the supermarket tabloids. (I choose to ignore the ridiculous bit about making her corpse look like she’s still pregnant when buried. What, like they know Sidious lied to Vader, and they decide to conspire with Sidious to maintain the deception? If Adywan ever takes on ROTS, maybe he can fix that.) The next time Vader is in the checkout line he realizes that he has been lied to. (He’s doesn’t go, “OMG, I can’t believe my master lied to me!” He knows that’s how Sith Lords work.) So he knows he has a kid out there somewhere, and decides to find out what happened to that child.
The child is not difficult to find. It’s a boy, and his name is Luke. The Larses are taking care of him, and Obi-wan is also nearby, looking out for him. He’s in good hands, may the Force be with him. Vader decides to leave him where he is. He may hate Obi-wan, but he wants the best for his son, and realizes that Obi-wan also cares about Luke, so he lets Obi-wan be so that he can watch over Luke. The last thing he wants is for his son to follow in his footsteps and become a Sith Lord, driven completely by rage and hate. It’s not a fun way to live. He’d rather Luke have a good, normal life, far away from the world of Sith Lords and Jedi. He may even meet with Obi-wan to make sure they’re on the same page about that, and they are. That’s why Obi-wan lives a stone’s throw from Luke for twenty years and never mentions a word about the Force or lightsabers to him until he needs help on his mission to Alderaan.
Vader does not know, nor have any reason to suspect, that Luke has a twin.
Sidious doesn’t interfere. Luke will not be brought up to know the Force, and that’s good enough. Sidious and Vader are a team, and killing your teammate’s son for no good reason is not good for teamwork.
Twenty years later, Vader is chasing an X-wing across the Death Star, and recognizes, “The Force is strong with this one.” Then, boom.
The next time Vader is in the checkout line, he sees a cover story about Luke Skywalker, the Rebel who fired the shot that destroyed the Death Star. He thinks, “Oh, crap. This is not good. Not good at all. We can’t have him out there becoming a Jedi and fighting against Sid and me. I’d better go get him. I’ll get him and turn him to the Dark Side. At least, I hope I can turn him, because if he won’t turn, I’ll have to kill him, and that would really suck.” So he sends out probes all over the galaxy looking for Luke, and discovers him on Hoth.
Not long after, he gets a call from his master.
“Hey, V-Man. I was just at the grocery store, and you’ll never guess who’s all over the tabloid covers!”
“Yeah, I know. Luke.”
“We can’t let him become a Jedi.”
“No shit, Sherlock. Don’t worry, I’m on it. I don’t have him yet, but I will soon. Then we’ll turn him to the Dark Side.”
“You realize, of course, that if he doesn’t turn, we’ll have to kill him.”
“Yes, I realize that. *Sigh.* We still on for Poker on Tuesday?”
“You bet. (Get it?) See you then. May the Force be with you.”
Time is running out for the Rebels. Antilles upcourt to Skywalker. He’s being paced by Darth Va— the bone-jarring pick by Solo! He came out of nowhere! Skywalker’s open from way outside, he launches at the buzzer... Good! It’s good! The Rebels win on a sensational buzzer beater by Luke Skywalker! Let’s take another look at that last shot. He just does get it off in time. Wow, what a shot. That’s why they call him Luke Legend.
That may be the most exciting battle I have ever been privileged to broadcast. Certainly the most dramatic finish. We’ll get you an update on the Artoo Detoo injury situation in just a moment. Right now let’s go courtside where SuperShadow is waiting with Chewbacca.