Originally Posted by Frosty
It would have been cooler if part of Anakin's slide into the dark side was his obsession with Padme, who rebuffs him and wants nothing to do with him. Luke and Leia could have been a product of Vader forcing himself on her, forcing her to flee and hide. This would have also fit better with Leia's recollection of her mother (implying that she didn't die in childhood).
There are countless possibilities yet Lucas picked the one that doesn't make any sense and virtually negated everything about the character that many people loved.