Lucas is a pretty interesting character as a filmmaker. His constant tweaking of the films is pretty unprecedented. Even Spielberg backtracked after that mess with ET and the guns. The problem is he's trying to shoehorn the original trilogy into the prequels. He obviously believes that the trilogy is flawed and that the prequels are closer to his original vision.
The scene shown is a great scene because Vader is quiet. He's in deep conflict inside and his body language shows it. Film is primarily a visual medium, which is why this works so well. He doesn't need to say anything. Everything you need to know is there. Adding a "noooo" is superfluous at best. At worst, it doesn't match Vader's character, who's been portrayed as cold and stoic, not emotional. As a viewer, it's jarring because it interrupts the flow of the scene.
But... I'm going to call shens on this. Vader's infamous "noooooo" scene from ROTS has been the butt of countless jokes for the last six years. Surely he knows. Lucas would have to be completely out to lunch to make that mistake again. Still, Return of the Jedi just keeps getting raped. I guess because it's the least memorable of the originals. I still feel sorry for poor Sebastian Shaw getting digitally cut out to extend Hayden Christensen's fifteen minutes.
