Ok,
First of all, the game is on "Schoolboy" level which is the easiest setting, so the AI teams are slower and you're much more likely to break tackles. HOWEVER, if you don't want to bust tackles anywhere near as frequent try the game on Seasoned, Legend and LEAGUE GOD modes!!!
Also, like others have pointed out, these vids were taken from an Unfinished PC version of the game, NOT, the final version.
As for the high tackle, I'll put the main play bit up where that particular tackle happened. You'll see that and AI defender grabs him, while the human player controlling the head high tackler, built up way too much aggression before hitting the tackle button, that's why the tackle is so over the top.
I can tell you now, I have played the game on PS2 and it is fantastic. It's more arcade-like than I was expecting, but it doesn't disappoint at all. I would say playability wise, it's like a bigger, better, faster, smoother version of Jonah Lomu Rugby and that is by no means a bad thing at all.
So to all those whinging about certain small parts of the game, wait until you play it before commenting, you'll see what I mean then!
In the meantime, boot up RUGBY 2004 and then you'll really have something to moan about