I think the 'side vents' in the out position simply deflect more wind out around your legs, helping your legs stay warmer by virtue of significantly reducing the wind chill factor. I guess the air coming out of the fairing back there has probably been heated by passing through the radiator, but my guess would be that at speed, there is so much air moving through the radiator that the air is not 'warm' but simply 'less cold.'
Of course when you are moving slower, or even stopped, the air coming out will be considerably warmer, and then it feels very nice...
I think it may have stopped snowing! Maybe I'll ride across town to the dealer after work, look at snowmobile gear (I think I at least need a new one of those breath-deflector things for my helmet) and ask them if they can put winter air in my tires. Or put chains on my tires.