While they were not called "cornrows" in pre-American contact Europe/Asia/Africa, they were certainly a valid way to do hair. People have definately done their hair in various experimental ways since we had opposable thumbs.
Mohawks were used by various Native tribes in America, and in several other places around the work. Other semi-shaved hairstyles are also known to have been used, such as shaving temples only, shaving the center/middle line of the top of the head, and shaving the front part of the head, and one of the traditional Chinese hairstyles of leaving a single braid down the back with the rest of the head shaved.
Cornrows, in fact, have been argued about the Venus figures from Europe, who were carved with a basket-like hairdo, or a basket on their head. It's not known weather it's cornrow or a basket, although many anthropologists refer to it as a basket-hat. In any case, it is still a valid explanation and hairstyle, and many of those figures date back to the early European Neolithic.
As to DR being based on any historical period, I think it would be prudent to mention that there are many items floating about that hint at modern-day, and this may be a medieval-mud, but it is a fantasy-medieval mud, so there's a lot of room for flexibility within reason.
I know this was an old post, but I wanted to add in my comments. I'm all for new hairdos, even though I play my S'kra more often. :P
