The problem I see is with the default settings in the camera (for JPGs) or the processor (for RAW).
Take the more recent Canon cameras as an example. There are various Picture Styles for JPGs. The default 'Standard' setting has a fairly S-shaped tone curve and quite high levels of in-camera sharpening and saturation. It's designed to make the photo 'pop' straight out of the box.
The 'Neutral' setting has a flatter tone curve (less contrast) and lower in-camera sharpening and saturation.
If you looked at a typical shot taken on each of these settings, the 'Standard' one would probably look better. However, the Neutral setting is safer because there's less chance of blowing highlights etc, and you can adjust sharpness and saturation in PP.
So someone could post a shot taken with a Canon 300mm f/4L (decent lens) on the Neutral setting, and it might not look as impressive as something taken with a Sigma 70-300 (no offence) on the Standard setting.
The same applies to RAW processing. Not only do people tweak the defaults to their taste, so there won't be consistency from one person to another, but there is often some background enhancement going on, which the user may not be able to eliminate. (For example, Rawshooter had quite a bit of default sharpening and some local contrast enhancement, quite apart from what you set it to.)
So it's a bit of a nightmare really!
