Oh the Qunari are like that do to time constraints, they intended them to have horns but they were too close to the sell date to change it, that doesn't make it any more right but it is a good reason. But I digress, there is an actual lore behind half-elves and their struggle of keeping their heritage a secret. Not only in the game, but also in the franchises other media sources like the books. One of my favorite ones was the Masked Empire and that was mainly because the character Michel de Chevin and his struggle to keep his heritage a secret from the rest of the world, if he didn't he would of lost his title as a chevalier and bodyguard to Emprise Celene.