I'd have thought that if you could damage a prop by pulling on it, any use of the engine (a large amount of horsepower being converted into thrust) would destroy it instantly. After all, the aircraft is pulled/pushed through the air by the prop in the first place. What do you think all those wire-locked bolts are for?
I can see the sense in pulling by the hub area, as it's the strongest part with the least mechanical advantage. Also, tying a rope to the tip and towing it with a car isn't the greatest idea.
I think it's one of those things that has grown over time from "take reasonable care when doing this" to "it'll come off in your hands!". There's another one doing the rounds about not checking the compression by hand because you might damage the engine. I hate to think what happens when the starter motor engages...
