I understand what they are saying, I just don't agree with it. You are assuming the entire movie public either knows everything about Superman or doesn't want to see a new origin tale of Superman.
I think people here are biased because they have taken in a lot of Superman and have seen his origin the way that they want, so they don't see a need to do it again. That is the same thing Singer felt and did which is why we got SR in the first place. Instead of starting from the beginning and telling his own tale, he just pick up from the place he wanted to in his Superman world that he liked. If you don't start over again, you are going to make assumptions about the character that may or may not be true for this version. We need to know why Clark chooses to be Superman just as much as why Bruce became Batman because he did not have to make that choice.