A lot of people are taught to aim for center mass. So might not be poor aim, might be they were taught to shoot for the wrong area.
I was taught to aim for a triangle area at the top of the torso... you'll be hitting heart or lungs that way.
I was also taught to aim for center mass, but I can see how your way would probably be more effective. Or like wolf_fire said, right between the eyes. And that would assume that you were not under stress and extremely accurate or very close.