If there are no examples of damage - is this actually an old wives tale?
At my club instructors regularly pull the planes by the props when the tow bar isn't handy (but I've always been told to do it at the root). Or is it that damage is likely to not be noticed? Of course, mags are checked and the prop isn't rotated when trying to pull it.
I do note that some prop manuals specifically state that you are never to try and move the aircraft by the prop. I don't know how widespread that limitation is (all the manuals I have looked at say this, eg
http://www.mccauley.textron.com/tech_guide.pdf page 10; or section 5B
http://www.hartzellprop.com/public_dl.php?id=4)