Simple put it`d be more realistic. I really hope a mod will come out for an even more well balanced game experience like you`ll be able to chop off limbs only when strike with a certain amount of strength, don`t you agree? Please support
this request if as it will not be that big deal and here are some very professional modders who could turn this game into an even more darker tone which will fit to the world of Skyrim perfectly.

It could`ve been a glitch but lower half of his left arm was missing and it was no slowmo killcam finishing or something like that.