The movie flowed too perfectly, that was another problem, but I won't go into that here (I think the film suffered very badly from pacing problems). But the point I'm making is that there are ways of introducing a movie. As I keep repeating, if you step away from the superheroes thing for a second, any movie needs to introduce its world and characters, and does so without doing an 'origin' story. The problem with SR is that the kind of questions being raised and the issues Superman was presented with (I would say faced, but there wasn't any character depth so he didn't actually face anything), with the exception of the 'son' thing, which was also badly handled, were superhero origin story issues. The whole acceptance and establishment thing. That's basically what this movie was about. It was Singer making an origin movie, and thinking that he could get away with saying that it wasn't one because he didn't re-tell the already well known Superman origin story.
And that's another point; the Superman origin story is well known. So when you say there is no need to 'remake' a Superman origin movie (which, by the way, isn't necessary - it's possible to make a brand new Superman origin movie without remaking anything; hell, by your reckoning there'd be no point in things like Birthright), it makes no sense when you go on to say "But with the characters and world being re-introduced, he had to think of people that dont know the Superman character that well (yes there are people like that out there)".
So, to sum up, and repeat the point I've been trying to make, Singer should either have made an origin film and restarted the franchise, or he should have gone for something completely original, and just assumed that everyone already knows the character backgrounds and history, vague or otherwise.
