Glad I managed to make it make sense!
We are humid here in the fall and winter. I imagine in the Midwest, venting a dryer might not cause people in the house to feel cold (remember that people are still keeping indoor temps in the 55-10,000,000 degree range but that extra moisture ventures into the wall to some extent, depending on which side the vapor barrier is (if it's there). If there is no vapor barrier, like in an older home, the moisture is going to condense in the insulation, and over time will degrade it's insulating value, not to mention encourage mold. Older homes also do not have a venting system to expel moist air that naturally accumulates from people just living and breathing, not to mention showers, dishes and cooking.