kyudo arrows have extra length for safety of beginners who don't know how much to draw at first and avoid hitting the grip of the bow, i seen this happen, dangerous and breaks arrows. also if the person doesn't have a good release they tend to draw more at release. the archer above is advance enough, hanshi("teacher of teachers"(wiki)) 8th dan, to probably not require the extra length.
Nope, just the exact perfect length :). I would not shoot with such a length myself since if you accidentally overdraw then it will be a disaster, but by the time you are a hanshi then you probably don't overdraw anymore, so you can just use exactly the right length of arrows.
well, I just made my own arrows and my sensei told me strictly, that they must be at least 5 cms longer than my arm (form the middle of my throat). And so does everybody in my club, the Dans too :/ So I assumed, that it is a rule. Sorry ...