It just seemed unnecessary to show Vader going into the suit. I had the impression from the OT that he had become who he is over the years, rather than in one fell swoop and then just remaining the same for 18 years while Luke grew up (while the Death Star was undergoing extensive testing?). All that stuff at the end of RotS was unnecesary. I know what happens at the beginning of Star Wars and I can fill in the blanks without being shown everything I already know and can imagine better.