Also you can see his torso inside his cuirass. Looks like Bethesda have gone back to Morrowind-style "Layering" System for clothes and armour!
Considering that in Morrowind, you COULDN'T see your body underneath your armor (Due to armor always placing individual body parts.), I don't see how you reached that conclusion, it's in Oblivion where some clothing and armor allowed parts of the skin beneath to be visible. If anything, I could see the fact that we can see someone's torso under the armor as possible evidence of no layered clothing in Skyrim, as I could see being able to wear clothing under armor causing problems with some armor that would leave parts of the character's body visible, but it's by no means a certain indication. Until Bethesda comes out and tells us we can or we can't wear clothing under armor, or we see a screenshot or gameplay video in which we can see a character's inventory screen, and we see both a piece of armor and clothing that covers the same part of the body equipped at the same time. A screenshot of a character who appears to be wearing clothing under armor wouldn't prove anything as it could simply be part of the armor model.
As far as seeing you're hair when wearing helmets, I wouldn't be at all surprised, since Fallout 3 could do this, I'd be rather dissappointed if Skyrim can't, and I hope that's the case. In the Elder Scrolls, I often refrain from wearing helmets because they just make my hair vanish, if Skyrim can avoid this, I might be less inclined to do so. I can't comment on seeing your face under full helmets though as we haven't seen any of those. Fallout 3 didn't do it, of course, but in Fallout 3, the fact that all the full helmets covered the wearer's eyes with a visor we couldn't see under might have something to do with that. Medieval style helmets though would generally have openings for one to see out of, in past games, these were just dark, but maybe in Skyrim, we'll actually be able to see the character's eyes under them, only time will tell.