Well yeah, the Macbook Air is lighter, so it would have less momentum when falling so the overall force provided by the surface on the Air would be less.
It's thinner, but then I'd assume that it would concentrate any force on it meaning the edges would probably be more prone to dents. I think the Macbook Pro's glass screen would be more vulnerable to breaking compared to the plastic coating and aluminium on the Air.
Also, the Air has less components inside, so I'd assume they're less prone to breaking than the Pro. Both have pretty standard hinges though.
Hmm.