It's hard to block the point after, for the ball is placed at the 3 yard line. Most kickers can kick from 30 yard line. But it can be blocked and makes a significant difference for the outcome of the game. I think one Superbowl was decided either by a field goal or a point after.
and 1 point after (kicking), no cannon shot for the point after. So one touchdown gets you a cannon shot.
And a field goal (distance kicking) is worth 3 points and a cannon shot as well. But that day there was no need for field goal as the opposition couldn't keep the host from marching into the end zone, either by rushing or passing.
At the end of the game, there was a sound off for the victory. BOOM! (刚才最后一响是北京时间20点整!)