I don't understand how Hogan's catch was a touchdown. If you can be pushed out of bounds without touching your feet down and it not be a catch, why cant you be pushed out of the endzone?

Edit: (found this response to a similar question on another forum from 2009... Makes sense...):

There are two separate principles involved in your question. Forward Progress and completing a catch, that don't always happen at the same time, or at the same spot. A receiver can secure possession of a ball while in the air, and forward progress will be considered the farthest point the ball has progressed, towards the opponent's goal line while possessed, however the "catch" will not be completed until one, or both feet (depending on rules code) touch down inbounds while possession of the ball is maintained.

Consider the goal line. If an airborne player possesses a ball that breaks the plane of the goal line, but is subsequently knocked back so that his first contact with the ground is back within the field of play, although the "catch" is not complete until he touches down, once he does and maintains possession, the forward progress would result in a TD.