About fifty years ago someone pointed out to me that four wheel drive only gets you four times as stuck. After watching a number of Yahoos around here driving 75 on snow covered roads and then winding up in a ditch later I can see the wisdom in that statement.

When Audi came out with the Quattro back in the early 80's they made it clear the reason was not for slick road traction, it was for dry road traction. They were trying to come up with a way to put 300 HP through a front wheel drive system and finally gave up on it. So they just used the quattro system they had developed for truck use and found that would not only allow a small truck to get around in snowy condition but would also put power down where it could find any grip at all.

By the way... With the quattro system they had then if you were in really slick conditions and the car could get no grip at all the tires would not spin. They would just not move since they had to have some grip in order to activate the system.