Why are "real" pictures better?

[El Diablo]

The picture thread someone posted today reminded me of this question that has been bothering me for a while.

I'm talking specifically of artistic pictures here, things that we look at and appreciate because they are beautiful/interesting/whatever to look at.

Over the past couple of years, I've seen a number of exhibitions of pictures where a big part of the appeal of the pictures is that there has been no digital manipulation of the shots. No Photoshopping, etc.

However, different chemicals, exposures, filters, lenses, and all sorts of stuff are used to create different types of effects on the final printed image.

Quite a few of these effects that are tough to achieve with photography are pretty easy to achieve for good Photoshoppers. However, if you put a bunch of the exact same printed images side-by-side and reveal that one set is "real" while the other set is Photoshopped, in my experience people tend to appreciate the "real" set far, far, far more than the Photoshopped ones.

So, given all of that, why is that? I mean, what is it that makes us appreciate the non-digitally-altered representation of something so much more, even though the image has been altered by the use of various techniques?