"Drink Upcharge" for milk??

Ok, I know you are asking... why is she showing up a reciept. I'll tell you.  On Sunday we were down near Richard's family and out visiting his grandmother.  We were running late for lunch and decided we'd splurge and get McDonalds.  Now I'm not a super health conscious person, but we eat healthy when possible so going to McDonalds is a treat not an every week/month thing.  When we go out to each the boys know to order milk/chocolate milk/lemonade or water.  At McDonalds Colby always gets white milk and Blake gets Chocolate milk.  Ok we order and don't even think of anything.  Then as we are leaving I glance at the reciept.... and I notice there is a "drink upcharge"  they charged $0.39 more for the chocolate milk and $0.40 more for the white milk.

Here is what it says on their web site that you get for Colby's Happy Meal:  A delicious cheeseburger with kids sized world famous fries, apple slices and your choice of fat free chocolate milk, low fat white milk or apple juice. 

Here is what it says on their web site that you get for Blake's Mighty Kids Meal: Six tender Chicken McNuggets made with white meat and comes with small size world famous fries, apple slices and your choice of fat free chocolate milk, low fat white milk or apple juice

I thought McDonalds was trying to appear to encourage healthier eating?  So why are you charging me an "drink upcharge" for the healthy drink instead of soda?

I know that $0.79 is not a lot of money, but when it is supposed to be part of the package, I don't want to pay extra... am I wrong??