What you say is true, but good microwave ovens have fine-enough power control to avoid any such problems caused by milk and also the problems caused by exploding eggs or exploding meat (which happens when you cook raw meat, instead of just reheating already cooked meat).

The great advantage of microwave ovens is that even if the first time when you cook something that you have not cooked before, you must experiment carefully to find the optimum time and power level for a given amount of food ingredients, once you have determined good values you can use them forever with perfect reproducibility and the food will be good every time and there will be no incidents with food exploding or overflowing in the oven.