Thats interesting and is something that I often think about, trouble is you see examples of it in country rocks too. I'm sure that in some cases natural channels caused by chemical & physical erosion may have been accentuated but I'm not sure wether this is always the case.
As you know yourself, if the mason selects the wrong stone or presents the wrong face to the weather then erosion will be inevitable - because Mr Newton proved it so.
If there are 'a family' of stones in a locality that display similar features, could that not indicate that this particular type of stone weathers in a certain way. I think proof of carving would be if stones of the same compositon in the same locality, with the same orientation i.e. bedding plans and stuff, did not show such markings.

Would that be Mr Goldsworthy? I do like his work, his Cumbrian pinfolds and stuff are beautiful but I don't think you can take all the credit after all stone walling has been around for quite some time.
If you want to see a truely Fitzcarraldian wall, check out the wall that runs up the easterly side of High Cup Nick, that builder must have really loved his art, or maybe hated his neighbour.

I have a study on Stone walling by Raymond Hayes that I think you'd enjoy. I'll send it to you when I leave the sea of nog