Ok I am not following what you are saying. We needed to know how Bruce became Batman complete with his training, yet we don't need to know how Clark became Superman including where his powers come from especially if they want to expand on the idea or make changes?
I don't see why that is a problem at all. It would be like doing a King Arthur movie but not show him pull the sword from the stone.
I think what people are saying is that Superman's origin has been covered A LOT in TV shows/movies about him, particularly in Superman: The Movie
, which gave us a very detailed, well developed version of it.
On the other hand, Batman was never given such an elaborate origin in a movie until Batman Begins
. Before that, we pretty much just got a view of Bruce's parents being killed and then jumping forward 20 or so years when he's already Batman. In the media, we were never shown why he decided to become Batman (he didn't have to become a costumed hero) or how he developed his skills and technology to become Batman. He simply was with no explanation. And for those earlier interpretations, such as the Burton movie, it worked and wasn't ultimately needed.
I think that is what people are suggesting for a future Superman film. As it stands, there really isn't any major reason to give movie goers another detailed origin tale. Other people in this thread are suggesting that maybe we are given an already established Supes, but have a quick flashback to his early life if the film calls for one.
Now, not doing a detailed origin would defeat the purpose of a Superman Begins
, so if that is what you are worried about, we can call it Superman: Already Begun, But Still Kinda New