On the subject of the 10m law: you can pretty much trace all the wrestling and attempts to control the ballcarrier beyond just bringing him to ground any which way to the effect of the early-90s change from 5m to 10m. See, it's pretty easy to be holding position up near where a tackle's being effected, and then get back 5m from it in time to be onside - but doubling the distance makes that impossible. You have to be moving backwards at a good rate of knots as the ballcarrier is being tackled in order to make the 10, or you're not getting there.
This changes a lot of things; most importantly for the issue at hand, it makes offloads absolutely deadly. With the 5m law, the defenders can hang around near the tackle to mitigate the effect of the offload. With the 10m law, they can't do that because they've got to be heading back to the referee, and suddenly when the offload comes in they're moving the wrong way and aren't organised.
This in turn leads to a change in tackling technique: now, instead of just putting the bloke on the ground, it becomes more important to tackle high and lock the ball up. All right, you might lose a few metres while the ballcarrier pushes himself forward with his newly-free legs until help arrives, but if he gets that offload away you're lucky if you only lose ten more metres - any offload is now a genuine chance of at least a line break, and probably a try-scoring chance. Additionally, you give your mates a couple extra seconds to make the ten, if they can go as soon as you've locked the ball up and there's help at hand.
And now it's taking longer and longer to effect tackles, and referees are constantly reminded to be vigilant for players slowing the play-the-ball after effecting a tackle, and people start thinking "what can we do to prolong the tackle process?" And that's where the modern emphasis comes in on controlling the ball, and then wrestling the ballcarrier in such a way that he falls on his back with his head pointing to his own posts; from that position it'll take him another second to be up and playing the ball than if he's on his front pointing to your posts, and when you're defending every extra second you can get is a precious thing.
So that's what they mean; it's entirely possible that if the 10m law had never come in, we wouldn't be seeing this exact flavour of dangerous throw, because the techniques that lead to it came about as a direct response to the challenges of the 10m law. Of course, now they've hit on the idea, you can't just go back to 5m and hope the teams will magically knock it off. Genies and bottles.
(The other thing that might be a factor here is an interpretation that was brought in on safety grounds; about ten years ago, instead of taking the ballcarrier to ground, what the defenders would have done is lifted his leg and then started pushing him backwards for field position until an attacking teammate could lend weight to the tackle. That was thought to be unsafe, so the interpretation came in that "held" should be called immediately the leg was lifted, and so defenders started trying to use the leg lift to bring the ballcarrier to ground in the manner shown here.)
Meh. One leg, both legs. No difference in IMO.
For me, the bit that makes this a stone red (if it had taken place in RU) is what Purple 16 does from 0:28 to 0:33, where, after already being at the tackle, he intentionally bends down, intentionally lifts the player up by a leg such that his head is below his hips and intentionally drives him head first into the ground. Whether the BC "ducks his head" or not, he was still always going to hit the ground head first.
For mine, this is a very dangerous tackle and a RC....all day log, every day!
It's always weird when someone you respect comes out with one of these "what on earth game are you watching?" interpretations of something that seems clear and obvious to you, isn't it? I wish more people would remember moments like this when they moan at video referees for coming up with a decision they don't understand.
, many would not and apply a literal reading. 
