I belive that the name comes from the medieval military the deadline was the point where infantry, or any group, came within normal range of the awaiting. In the urban situation a line would often be drawn across a plaza any unauthoized person crossing the line would be dead.
One of the earliest meanings of 'deadline' was an actual line drawn around a prison's perimeter, beyond which a prisoner, if spotted, would be shot at and possibly rendered 'dead'! It became associated with a cut-off point in publishing newspapers only in the 1920s. Perhaps the same sort of thinking lay behind it...the journalist had better not overstep it or he'd be in trouble.