Okay, here we see an 8-story stone tower, consisting of a ring of walls on the ground and a single wall with a single staircase beside it. Inside the ring are a bull, which is chained to the ground, and a legendary armorsmith, who managed to wall himself up with the bull. Note that neither of them can possibly escape that square, and so any blocks falling into the square must necessarily hit either the bull or the smith. (You can't see the smith in this picture, but trust me, he's there.)
3D view of tower:
I built and then deconstructed the floor 8 levels above my two
unfortunate victims test subjects five times in a row, dropping marble blocks down onto them from a dizzying height. However, as you can see, both the bull and the weaponsmith remain completely unharmed.
You can clearly see here that five marble blocks are laying on the ground underneath the smith and the bull.
Now, I hadn't seen Deathworks's post when I made the experiment, so I did indeed have the bull chained to the ground. However, if the chain had any effect on whether a creature can be hurt by a falling block, then it would have protected the bull, but not the smith. Unless somebody else can post evidence of a falling stone block's ability to hurt creatures, I think we can declare this myth BUSTED.