"accustomed to certain movements" ... that they will have to use on some level in a real fight or else the practice is pointless and would have never been developed at all. The perceived skill of the people in the video is utterly irrelevant and I didn't even look at their faces. Of course they're having fun, it's their hobby and completely unnecessary in 2015.
Something similar can be said for fencing. The techniques they use don't exist in a fencing vacuum. Existing (real) fencing techniques just become more prevalent in the sport because of restrictions placed upon them by the ruleset.
In the video you showed me, each time one fighter wants to square off with their opponent, they take a large retreating step (impossible in warband). Bear in mind this is a duel in a very controlled environment with various contact rules. In a large battle, sometimes you are outnumbered, requiring skilled evasion to escape certain death, perhaps to rejoin your force, kite the enemy or reach an advantageous position.
Video games are also not analogous but in the opposite way, in that everyone is essentially insane with a death wish because of the lack of consequence. IMO this makes evasive techniques all the more important, as players will kill their teammates to reach you or leave themselves wide open with arrogant blind flurries.
Evaision, dodging, dashing... it's all about moving into space. It allows you to have more control over the pace of a fight. Without it, you are a slave to the speed or attacks, parries, move acceleration, e.t.c. dictated by the programmers. If you think about Dark Souls or other games that have you fighting massive beasts... you are at an inherent disadvantage and spend a lot of time rolling around to escape giant smash attacks or whatever. Well, do you expect every fight to be evenly matched in a melee combat game, or every moment of every fight? Sometimes you need to GTFO, or go under or go around. It's just a natural. I mean, ****, are you going to just stand there if you're about to get hit by a train. No, you GTFO.
And if you can't bend your knees, or bend at the waist. Where is your power coming from? It goes feet, knees, hips, back, shoulders, head, arms... roughly in that order.