The door thing is brought up a lot, but if you lived in a climate with very cold winters, you would want a shorter door to keep in more heat. People just ducked a bit coming into and out of houses. (Another reason that hats were taken off before entering a house.)
They didn't shrink the people to put them in the coffins...
Nor did they lower the ceilings just so I could stand (5'6") but my friends had to bend...