I did some looking and
Howstuffworks "How Humidifiers Work" explains it the best I think.
I was thinking maybe wind chill factored in humidity, plus another person posted on Metro's thread about him being cold in his apartment having to do with humidity, but I guess I was right before - more humidity = feel warmer due to decreased rates of evap. from skin.
I have my humidifier set at 40% now - probably should set it a bit lower because on really cold days we get condensation on the walls of our noninsulated plaster-walled living room. Something to fix for next year...
So.. Crank that humidifier back up!