I've always thought fully armoured fistfights kind of weird. I mean, the effect of a punch on a bare face is really the intent. A gloved fist against a metal face - unless the person's head inside gets a heavy jolt against the inside, they're not going to bruise; at worst, they might get a little dizzy-phased, but especially with mjolnir, the armor I would expect to absorb the blow. Tho at the same time, the gauntleted punch is augmented by the armour, just as the head is protected by a super-strong armor.
Anyway, point being, the effect of a fist punch between two fully armored combatants would be different than bare-knuckle to chin.
More like, the intent of a fist-fight between machines wouldn't be to damage the body so much as destroy the armor and machinery. But I suppose when you enter into melee combat your natural instinct would kick in and you fight as if you were bare-fisted. *shrug*
But yeah, it's always felt odd to me watching it as well...