When I shop at the supermarket and pick out a gallon of milk I always check the 'best by' date. If I search in back I will usually find a gallon with a date that is the furthest out, which means it is the freshest. The store rotates their stock by putting the oldest in front. I don't remember a time when I reached for a gallon of milk and it had been expired, but I always check the date. Not to insinuate that milk beyond its expiration is necessarily spoiled, but I certainly would not purchase it and I don't think selling expired milk is anyone's expectation, not the dairy farmer and not the store owner.
So why is expired beer on the shelves and sold, regularly?