Imagine you are playing one of those spaceship shooters and suddenly a death ray that spans the width of the screen appears, no matter how skilled you are there is no way you are ever going to escape that death ray. That, is how the headshot is in New Vegas, you could be annihilating a group of legion soldiers, they could be almost dead and you could be at 70% hp, but 1 bullet, just 1 single bullet, could bring that 70% down to 0%. I play on very hard mode and it may not be like that on easier modes, but the point of high difficulty isn't for random unescapable death rays, the point is to make the game more challenging.
Sorry if i posted in the wrong section.