Personally, I still don't see how that line changes anything, even with ROTS. Vader learned of Luke after the BoY. This insinuates that he's hiding this knowledge from the Emperor, and I don't see the point. With ROTS, it goes like how I said above. "Search your feelings, I lied." One wonders why Vader didn't lash out there, or at least ask why.

Not to mention the line reading by McDeirmid was awful. I can't stand that "YEEESSSSSSSS". It comes off as a, "Why didn't I think of that" moment instead of the, "Interesting suggestion" of the original, "Yess......yes". It just felt totally out of character.