A camera is never going to capture what your eyes see, because it can't adjust as finely. Take this picture for example:
That image is actually two combined - the background and the foreground are separate. It's not an HDR, exactly, since I did it manually using gradients and the fuzzy paintbrush tool.
The human eye can adjust and see a blue sky and brown bridge and grafittied building just fine at the same time. But a camera can't, either the sky is white or the building is black. A camera just can't replicate real life that well.
Same goes for colour saturation - to a point. I generally like to turn up sliders too far - I'm a fan of bright colours and contrast - but a standard camera (or even a good camera) can't get the colours exactly as they are supposed to be. Sometimes it doesn't properly determine which colour white is, sometimes it doesn't get the brightness right, stuff like that.
There are a lot of people who argue against post-processing in any way, but in my opinion it is, at least in part, a useful tool to make a picture real.
Keeping in mind that I like mine surreal, to a point. Although the example in this post isn't so bad.
