calico, the example you linked to in your initial post is great. However, if you click to enlarge the image and see it larger it is very obviously a painting (a good one, I'll grant you) It only looks photographic at the smaller size. Another example of this is
http://stacey73.deviantart.com/gallery/#/d7ziyp (by a lovely, and very funny woman)
Many many years ago I used to do this type of thing for a living, but with "real" paintbrushes, airbrushes, pencils etc etc as I'm a Technical Illustrator by training! The First thing you are taught is "ALWAYS illustrate for reduction" eg. if your illustration is going to be printed in a book or magazine at 100mm x 100mm the actual illustration would be at least 200 x 200 more likely 300 x 300. I have produced work that when reduced is indistinguishable from the photo reference used, but if you see the original, it's very obviously an illustration, and I think that the same can be said most of "Digital" illustration too. You only ever see these images at a fraction of their painted size. A lot of the skill in this is knowing what detail you can "leave out" or fudge in the full size version and still have it look photo real in the reduced version
