Micellar Casein is not skim milk minus the lactose. Milk protein is approx 80% casein and 20% lactalbumin.
Since milk is a multiphasic, i.e fat,casein,micells,lactalbumin and in colloidal suspension, isolating any component in an undenatured form is very expensive and time consuming.
Whey products are easier because of their availablity after other uses, like in cheese manufacture, but micellar casein is extracted without acid.
Casein has many uses, I mean some of the stuff that oozes out of your chicken in the pan is often a sodium and casein mix. Its also used in Ice Cream manufacture sometimes.
Traditionally casein is isolated by a low pH precipitation method. By this method there is a considerable loss of the target's therapeutic benefits, for example denaturisation, damage of protein structure and a resulting lower biological value.
By replacing the acid precipitation method by more gentle techniques like filtration (micro/nano) the protein is not damaged. No acid or heat is used.