For large breeds, the amount of calcium intake while a puppy is important to moderate their bone growth to prevent skeletal problems. Adult food doesn't have the same requirements. Also, I think puppy food has more calories to accommodate their rapid growth periods.
All commercial dog food has an additive package, it amounts to them mixing up the food ingredients and then adding the supplements. I think the difference is the quantity of supplements. There is nothing special about puppy kibble which makes it good, its all crap.