I don't understand Rugby, Australian rules, or Gaelic football especially well (or US football for that matter, though I've watched it casually over the years), but my understanding is that tacking in these sports has a different purpose and that tackling technique reflects this. You may be on to something with you comment about yards - in American football, it can even be a game of inches. As a result, tackling isn't a way to halt play or stop someone, or to transition during flow of play - you need to essentially completely halt that person's forward movement without even giving an inch.
I've thought this may be why American football has more of the full body collision, where two (very large and powerfully built) men collide at high velocity almost horizontal to the earth. They're trying to gain as little as a few inches in the collision.
I've heard complaints from Australian rules players who come to the US about tackling - that the way US players have learned to tackle doesn't have much strategic value and greatly increases the possibility of injury, buy they continue to tackle this way when they join Australian rules leagues.
That's what I've heard and thought about, I do want to be clear that I don't know too much about all this - what I've written is more of a question in case someone in the know could weigh in.