Powdered milk is also made from pasteurized milk. The main difference is that it has already been dehydrated in order to make this last longer. Fresh milk is known to be liquidized milk. This would need to be refrigerated, especially after you have opened it because it will spoil faster as compared to powdered milk.
Some people may think that powdered milk is not real milk, but most of the products that you will see are still made out of real milk. Some of them may have just been added with other ingredients in order to add to the weight of the milk. Powdered milk can be stored longer at home as compared to fresh milk.