I think Lucas is wise in sticking with relatively unknown actors. Better to have people saying, "Oh, Anakin from the Star Wars movies is in this new movie" rather than, "Oh, Batman is playing Anakin in the next Star Wars movie" (yeah, I know I am a bit anachronistic there).

When you use a known actor, he already has an identity in the audiences mind. If you go with a relatively unknown, a few people will have seen the TV show he was in, but for the vast majority of the audience, you and your movie will be creating his identity, assuming your movie is an big as Star Wars that is. Harrison Ford will be either Han Solo or Indiana Jones until the day he dies, no other role will ever change that.

Besides, Bale seems to have become the default go to guy for dark brooding hero roles. Glad he wasn't grow'd up Ani, it would be like casting Harrison Ford as the hero in an adventure film like The Mummy, it is too easy of a casting choice and it becomes redundant. Of course, if he had been cast in Ep. II, it would have been before Batman, which would mean someone else would have played Batman, and that would have sucked. Definitely could have done better than Hayden, but I don't think Bale was the man for the job.