D&D 3rd edition is terrible at beeing simulationist. It has spells to regenerate lost limbs, but no way to actually lose a limb with any rule. And it is so strictly ruled that at i hesitate to invent such a rule, because it seems like cheating to me.
If the rules are more general, more exception based with streamlined rules, it seems to be much fairer to make exceptions, because 4th edition is based on them.
You want a trap to cut a limb, n.p. exception to the general rule. You want a player to cut an enemies limb, np. exception, but a very very hard task (somethink like -10 to hit). Why does it work with 4th edition: -10 is equally penalizing at every level. In 3rd edition -10 at level 10 usually is a joke.
So conclusion: As 4th edition seems to be more gamist than 4th edition, it
a) seems to be coherent
b) seems to be easily adjustable