Explains why my Dunmer and Altmer characters can use it...
Pretty sure anyone can use the Thu'um with enough training and dedication, like in Ulfric's case. If anyone is treating the gift from the Gods badly, it's Ulfric for using it the way he did; to make a political statement.
Dragonborn != Tongue. The Voice was the gift from Kynareth for the nords. Dragonborn seems to be a gift from Shor or Akatosh(Maybe both)
Though it doesn't necessarily preclude other races learning the Voice, they just never have. And the Tongues never took non-nord apprentices in the past.
http://www.imperial-library.info/content/evening-star-3e-432
Jo'Hamiir seems particularly intrigued by the demonstration and asks if anyone can learn the thu'um or if it is something only Nords (and Atmorans, if any survive) can do. Svontilda does not know, as she's never seen anyone other than a Nord trained in the thu'um. She speculates that anyone could learn to do it, and while it would be unusual for a Tongue to take an apprentice who is not a Nord, she does not know of any traditions that would prevent it.
Okay, before I argue, I have to ask you something since I've noticed you all over the place and you really seem to know the history and canon (no, I'm not being sarcastic - you are like the ultimate reference for all things TES): where are the rules for such a duel described (if at all)? Because I'm thinking that like in a swordfight - you can't use a firearm; or a UFC match - you can't eye-gouge; or an arm-wrestling match - you can't use two hands - so in this challenge for the seat of high King, are you saying it's a free-for-all, like, anything goes? What is the basis for your statement that they're allowed to use "(anything) at their disposal"? I just assumed the idea is that the opponents have a certain set of rules or restrictions. If anything goes, couldn't Torygg have ordered his, let's say, archers to cut down Ulfric before he even reached the High King, since his archers are just an extension of his power just as the Thu'um is an extension of Ulfric's power? The idea of an older experienced warrior picking a fight with a kid, and then using a magical power that wasn't even available to Torygg isn't very noble, nor does it really establish that Ulfric is a better warrior - he didn't even actually fight him - he incapacitated him with magic and then - I'll use the word again - murdered him. And if it's all fair game, and everyone knows this, then why did Ulfric flee the scene?
The duel is person vs person, no outside influence as inferred from everyone who talks about it. To be honest, "Nords Arise!" is the only source I have on it that isn't word of mouth. I'm mainly going off of testimony of those in game and the nord tendency to revere the use of thu'um in battle as just.(PGE 1st and 3rd, children of the sky, etc...) As well as the description of the thu'um as being an extension of yourself. Torygg was likely in his early to mid 20's btw.
The use of the thu'um was not meant to show nobility, it was a wake up call and reminder of nordic abilities. Ulfric had to flee because Elisif freaked out when Torygg lost. She ordered his arrest. The imperials unknowing of the nord laws or unwilling to accept them(Despite them using duels to settle leadership disputes too) obliged. Ulfric wasn't about to let the empire screw him over again so he fled.(See Markarth Incident: Empire pinned everything on Ulfric despite all the evidence pointing to Igmund.)