Keeping in the spirit of the comic books...telling and re-telling the origin of a hero is a time honored tradition. Comic books are all about re writing fictional history constantly.
Actually, this is probably the closest Hollywierd has come to showing Batman's true origins. Sure he and his parents went to the opera in the movie instead of "The Mask of Zorro" as depicted in the comics, but if I had a couple hundred billion laying around, I'd probably go to the opera and then go home to watch a private screening of "Zorro".