ExploderWizard
Hero
Called shots is one of the many ways in which people try to cobble fiddly bits of combat sim onto an otherwise completely abstract combat system. It doesn't improve the game.
BAZINGA!
In a game where a "hit" isn't the result of swinging a weapon and "damage" can be sustained without a "hit" taking place, is getting even more specific with regard to the effect of a "hit" really a good idea?
Such things have their place in less abstract combat systems. I like being able to thrust to the vitals for MORE damage, or slash the leg to cripple/slow a foe in GURPS combat. There is no ambiguity going on there. An attack IS a single thrust or slash of a weapon. The damage caused is quite physical indeed. Called shots make sense because they mesh well with rest of the combat system.