I will have to find the quote, but Lucas was asked when they were filming TPM if Spielberg would direct Episode II & III. Now I am paraphrasing but he said, "Spielberg has alot of great movies: Jaws, Jurassic Park, ET, etc, but Star Wars is my baby."
Pretty much Lucas is saying that HE is known for Star Wars, and Spielberg has enough great movies to be a part of ANOTHER great movie series.
Thats why I found the revelation that Spielberg was going to direct Jedi in the 2004 documentary seemed out of nowhere.
Ok, maybe George didn't ask Steve to direct one of the prequels, Geoge was in complete control of those atrocities. No outside opinions or steering at all. And we all know how that ended up... But we're talking Jedi.
And why would George want this information in the documentary (and don't fool yourself into thinking he wasn't in control of it's content) if he was running around saying that he never asked Spielberg to do it?
Spielberg saying "Star Wars is Georges baby" makes a lot more sense. It's polite way of saying no.
Then again, George has been caught in so many lies that finding out that the Spielberg to direct Jedi story is false would hardly faze me.