I would suspect that sparring in a martial arts context - the product of years of training and practicing specific, restrained moves, in which the objective is not to harm the opponent but to demonstrate superior technique - is rather different, emotionally, from a life-or-death struggle or even a fight between two combatants working off instinct and experience, neither of whom have been conditioned to associate that particular kind of fighting with a safe, controlled environment.

That said, I agree with you that there's a matter of individual variation. The people who receive the strongest adrenaline high from fighting, however, are probably not the ones asked to return to the martial arts academy.