Why: Up until the BluRay version, Vader was seen as having an internal struggle with himself on whether to help out his son, or whether to be loyal to the Emperor and watch his son die a painful death. Now, that internal struggle isn't so internal anymore because we hear Vader say "No. Nooo!" as he makes his decision to kill the Emperor. The problem with this is that, not only does the new voice sound really corny, it also devalues the meaning of that scene by making it too "in-your-face" and eliminates all traces of intrigue. And for such an important event in the Star Wars saga, it's really a shame to destroy something that everyone has watched and loved up till now. Final decision: get rid of it!