Puggo - Jar Jar's Yoda said:

... the relationship between Vader and the Emperor was much more scary when we DIDN'T know all the crappy PT backstory. We see how horrible Vader is, and everyone concerned says he's nothing compared to the Emperor, who spends most of his time shrouded in a hood. But in the PT, Vader is a whiny young brat and the Emperor is essentially a power-hungry crazy guy they goes all Gollum in the process. Sometimes less is more.

Bingo. Lucas answered questions people weren't asking.