You make this sound like there are no OL blocking. We're talking about BEHIND the line of scrimmage. No one is saying you can't hit anybody down field. What Parcells supposedly was implying is that you hit the QB behind the line of scrimmage whether he keeps or give on EVERY play. That would be easy to do if there were no offensive line blocking.
On a lot of read option plays ONLY the LB is left unblocked. His assignment is to get to the BALL(not the player). He can't get to both the QB & RB at the same time.
watch this: http://www.youtube.com/watch?v=bDu-livhN-k
Now if the QB gives to the RB instead of keeping it then that LB will go after the RB(only makes sense, right?). In Parcell's scenario who would be assigned just to hit the QB on that every play?
Unless 2 players are left unblocked. And of course that would be stupid.
have you ever played in a college option offense? I have a strong inference that you haven't. It is perfectly legal to hit the QB on every play wether he hands the ball or not. As long as the QB is not in a defenseless position (having just thrown a pass) everything else is live game.
In this video that you provided:
Neither example shows the LB being the read. The first one uses the DE and the second one uses the DT.
As far as the LB being the read man it just depends on the blocking scheme, but I've never seen anyone run a dive/read option using the LB as the read. Like I said before USUALLY the DE is the read person because he is the easiest person to read. When you are running a play like this u want to make the QBs job as simple as possible.