If the images are properly exposed, why do they require +50 brightness...? Shouldn't it default to 0 brightness?
Rick, the problem is that our visual system (eyes and brain) do not respond linearly to light energy, unlike digital camera sensors. Even with a well exposed image, a tone curve adjustment is required to produce an image that appears more natural to the human eye.
You can turn off the brightness portion of Camera Raw's tone curve entirely by setting Brightness to zero. However you'll probably find that the image doesn't look so good when you do that.