I'll add that "as long as it's stored at correct temperatures". Milk and dairy products need to be kept between 32 and 38 degrees. Once it gets above 38 degrees, the natural bacteria starts to grow and eat the product, producing the "soured" taste. If milk sits out and gets above 38 degrees, it'll actually start knocking days off and can get "sour" before the printed on days.
You can always tell a good grocery store by observing when your milk starts to sour. If its before or right at the date, they've let the milk sit outside the cooler for too long. If you're getting 7-10+ days past that date, it means the milk has come off the cooled truck and right into the cooler and stored away from the door/light.
Light is also a big contributor, which is why your fridge's light will go out when you shut the door.