Think about it this way.... There are (for easy math..) 10 stops of information in a raw file. What you see in the preview will be an average of those values.... a 5. Any given detail in an image may be brighter/darker.. more colorful/less colorful than what you see in the preview. When you edit you are cutting away the extra information so what you have left in the jpeg is what you "saw" in the scene according to your eye. The raw gives you that material to cut away. Shooting in jpeg, the camera does that for you, and leaves you little material left to trim to your liking.
