I don't think it's a huge difference. Basically, the conversation was tweaked just slightly:
Old:
Darth Vader: [kneeling before Emperor Palpatine's hologram] What is thy bidding, my master?
The Emperor: There is a great disturbance in the Force.
Darth Vader: I have felt it.
The Emperor: We have a new enemy. Luke Skywalker.
Darth Vader: Yes, Master.
The Emperor: He could destroy us.
Darth Vader: He's just a boy. Obi-Wan can no longer help him.
The Emperor: The Force is strong with him. The son of Skywalker must not become a Jedi.
Darth Vader: If he could be turned, he would become a powerful ally.
The Emperor: [intrigued] Yes... He would be a great asset. Can it be done?
Darth Vader: He will join us or die, master.
The tweak in the retconned version (See DavRobo60's answer) basically avoids any questions that would arise among people who knew the backstory, regarding Vader's lack of surprise in the original conversation. There's"There's a new Skywalker running around? But the Skywalker name died with Anakin.!" By giving him a couple extra lines to express surprise, you hang a lampshade on it and move on.
Either way, if this were the first time you ever saw the original trilogy (and hadn't seen the prequels), the huge surprise (that Darth Vader IS Anakin Skywalker) is still safe; there's just a little extra surprise that Anakin Skywalker had a son that Vader didn't know about.