In mineralogy, hardness is the characteristic of a solid material that relates to its ability to scratch softer materials. A mineral can only be scratched by a harder substance. A soft material can never scratch a hard material. This is actually only one of several definitions for hardness in the broader science of Materials Science and it is sometimes specifically referred to as 'scratch hardness'. There are also numerous scales used to measure hardness, but the one most commonly associated with scratch hardness, and the one seemingly used by ASUS, is Moh's scale of mineral hardness.
Looking at Moh's hardness scale, we can see that Sapphire is a 9 on the scale, which corroborates ASUS' claims of the LS201's screen's hardness. A closer examination of the fine print in the marketing materials also reveals that the LS201 has been tested with the ASTM (American Society for Testing and Materials) D3363-92a pencil hardness test. The D3363-92a is a fairly standard test of material hardness and it is proof enough to us that ASUS' claims probably have some substance. In any case, you can definitely bet the LS201 is more resistant to scratches than your standard LCD screen made of soft plastics.
We felt the You Tube video that attracted us to the LS201 in the first place was proof enough of its durability so we did not go out of our way to test its mettle. However, we did give it a couple solid blows from an old keyboard we had laying around for good measure and it withstood the punishment without even blinking, literally. The screen was displaying the desktop at the time and the blow didn't cause it to distort, blink or change in any way, nor did it leave any lasting scratches or marks.
We think that this is a sufficient test of the LS201's durability and we felt no need to fire crossbow bolts at our review sample. Especially since ASUS doesn't make any specific claims about the LS201's crossbow bolt deflection ability. In all likeliness, the worst an LS201 will experience at the hands of its user is some undue venting of frustration, most likely with office supplies or a keyboard as in our "test", and not medieval weaponry.