Weapons take excessive damage when striking while falling from height

I lost an un-used iron sword giving a coup de gras to a creeper from about seven blocks up. I'd weakened the creeper with two arrows and then dropped on it from the roof of my house. I successfully landed a critical hit, killing the creeper but destroying my iron sword.

Does the initial height of a critical hit inflict proportionally increased wear? It seems like this should be capped, so a new weapon is not destroyed when falling from such an insignificant height.