I wouldn't exactly say it's done on "purpose". RAW images are soft due to the anti-aliasing filter on the sensor. This reduces the sharpness of the image in order to reduce aliasing in diagonal lines and Moire in details that are fine and repetitive.
I think it is a good artistic exercise to be minimalist -- to try to get along without PS -- to improve your skill as a photographer, not just as a technician. But, as Mike30D points out, those of us who shoot in RAW need sharpening tools. I kept getting comments that my images were soft until I learned that. I was pulling my hair out trying to figure out what was wrong (and I have less and less of that hair to afford to be able to do that).
mmm... actually the softness isn't a RAW issue, it's a digital one, and technically not on
all cameras, but certainly on most. Most cameras have a filter/screen (can't think of the name at the moment) that's placed over the sensor to essentially average out the colors on the pixels. It has a softening effect, but avoids moire and stepping patterns that would be the result with out it.
To OP: I used to agonize over this a bit, but I gave up. There are a few things to consider.
1. What is your art? Photography is an art, but then so are some of the amazing things you can do in Photoshop. Do I call a massively modified picture a good picture? No... I might call it a neat piece of art, however.
2. There are some limitations in digital for which Photoshop is an answer... such as the sharpening situation. The simple fact is that we're using a digital item* of relatively small size to represent a very "analog" scene of reflecting light... when you have "unlimited pixels" being represented by "limited pixels" yer gonna have you a problem. Gotta compensate somehow...
3. What's cheating, really? Think about this for a moment. I use Photoshop. Is that cheating? Hell, I use a digital camera and can take nearly unlimited pictures with instant "development" and see my results and make adjustments... that seems kinda cheating over my old AE1. But then my AE1 Program had auto-exposure settings and a computer on board. That seems kinda cheating over the full manual Canon my Dad had. But hell, his camera had a roll of film... that seems kinda cheating over the slide-based job his grandfather had... don't we drive cars to work? What's this telephone nonsense? Pavement? Forced hot water? Fire? The Wheel?!?!?!!? WHO ALLOWED THIS WHOLE WHEEL FOOLISHNESS!?!?!
Kinda silly, I know... but think about it. 50 years from now you'll be telling your grandkids that whatever photographic technology they are using is cheating, and you'll hearken back to the grand ole' days of Photoshop CS3 and your 12 megapixel DSLR.