NOT BEHEADING... just an icon, like the head shot icon for a bow shot, but for melee.
Of course it's not "needed".... one could make large lengthy arguments about many "needs"- my idea though is pure vanity.
You didn't think that vanity was a minor thing that coalesced nothing of satisfaction did you?
And pray you did not forget that a large collection of small and apparently insignificant things can add up into the total system of rewards that motivates play..........