Tennessee said:
I've always thought the stupidest rule is if the WR has possesion, and the WR was going to come down inbounds, but the DB forces him out of bounds, it is still a catch...
To me that seems like good D...I have never understood why that rule is there
It seems ridiculously extreme, I know, but that rule prevents the following situation: A small wide receiver (Prothro, Palmer, Joey Jones) leaps to make a spectacular catch near the hash marks toward the middle of the field. Before he hits the ground, a linebacker wraps up the small receiver, slinging him over his shoulder and proceeds to carry him out of bounds before letting him drop. Without this rule, the call would be "INCOMPLETE PASS."
I know it is ludicrous to take it to that extreme. Such an occurrance as I described would be an unbelievable feat in and of itself, but at some point there is a threshold between that scenario and the one you described (the receiver is near the side boundary and gets pushed or carried out of bounds before touching the ground.) It would be difficult to require a referee to make a judgement on how far from the sideline that the pushing or carrying could legally begin, so (I think) the rule is that if it appears the receiver would have landed in the field of play if not having been pushed/carried, then the pass is complete.