I can believe it.
I try my very best not to use any PP other than maybe an occasional exposure tweak or horizon correction. Although, I recently bought LightRoom and I can see how tempting it is to start playing around with stuff. But I still try not to use it as much because I find myself playing around with the colors too much, almost to the point of making it unnatural. But I have seen many great artists on PS and LR, it's just not my thing. Can't even imagine how amazing PS would be.
Now I do use customized settings on the picture styles in the camera to help me achieve the look. Orange/Red filters on black and white. I'll boost contrast +2 on complex landscapes. And I usually shoot +1 saturation on my 5d and +2 even +3 on my 30d.
I've actually seen people say this is cheap or cheating? But at the same time it's okay to move the contrast slider in LR, DPP, etc. afterwards. Don't understand that comment. If I know I want a high contrast shot when I take it, and actually understand what contrast does, why not set the camera up that way when I shoot it. Saves me time later on.
I've also found a CP filter and GND square filter are huge for making pictures pop and giving them a wide dynamic range. This shot is SOOC:
Camera was set with +2 contrast, darkening filter and I also used a CP filter and a GND angled to hit the sky and darken it a further 2 stops.
I see the same type effect on a few of the shots from the above posted website.
It is curious as to why he would have PS saved files, but it's not damning. He could be using PS to add borders, overlay copyright info, signature, etc. Also could be for horizon correction. For instance, I primarily bought LR because DPP does not have a horizon fixer. So if I'm off, I have to use a lossy format editor to fix it and the file starts to degrade.
I'd say from all my shots on my website, only about 10 or so were color/contrast manipulated in LR. Another 10% had what I would call heavy processing from DPP. Correcting major exposure snafus (i.e. more than .33 stop in either way), changing white balance, playing with contrast, etc. The rest are as is from my custom settings in camera and added use of filters.
Here's a few more examples:
