The 2004 version was to re-establish continuity with prequels. But my theory is, Vader knew about his son since ANH and probably didn't want the Emperor to know. Why? Well, like Luke said "I know there's good in you. The Emperor hasn't driven it from you fully. That was why you couldn't defeat me, that's why you won't take me to your master now." The good of Vader/Anakin didn't want his son to turn to the Dark Side or else Luke would become the very thing he was trying to stop. Simple is that.

Sometimes when it comes the SE, I can be veeeery protective. ;)

And cap I like your Emperor calls Vader in the first post. It could make a good Robot Chicken sketch and yes, I do get the Poker joke.