You also have to remember, the games are different. I will state now that I don't know much about either Aussie Rules (which I have watched hours of, but still can't see a structured game - it just seems like and official version of the playground game "Smear the Queer", which, of course, is not PC, but that is what we called it when we were kids) or rugby, but I have never seen the type of tackling that goes on in the NFL. It seems to be more of a "running grab, pull down, try to get the ball", where the NFL is "stick your helmet in his chest, wrap up his legs and drive him into the ground."
[edited to add]
Oh, and once the player passes the line of scrimmage with the ball, there is very little he can do to get rid of it. He is getting tackled, without the luxury of getting rid of the ball when it looks like he is going to get hit.