Dd has always worn a little cami undershirt when it's cold. Dh wears them year-round, and my mother does too. It's not that much more laundry... it takes me less than 5 extra minutes a week to deal with them and they keep my loved ones more comfortable.
I don't wear them because I'm warm-natured. I wear short-sleeved t-shirts even in the middle of winter and shorts around the house... and keep the house at 66F in the winter (which is probably why they want the undershirts ). Dh is from a very hot, formal middle eastern country... and he's on the downward slide to 60, so is also a generation older than most people here at MDC. Everyone from his home country wears undershirts.