I think it has much to do with the dual use of the term 'fat'. There is fat in the food you eat, and if you eat too much food, you may get fat. However, fat you consume doesn't become fat any more readily than other food. From what I recall from biochem, carbohydrates are actually more easily converted to stored energy. It's not as if your adipose cells are directly stocked with the fat that you put in your mouth.

If you really want skim milk, buy a gallon of whole milk, add a gallon of water. Boom. Half-priced skim milk.