Food Prices

Tosay after returning from the Ninrty Six Revolutionary War Battlefield at Ninety Six, South Carolina my brother and I paid a visit to the local Bi-Lo. While shopping I bought a store brand gallon of milk. Directly beside of it was a gallon of Pet milk that costs $2.00 more. I wondered why was it two dollars more for the well known brand. Does anyone have a reasonable idea here ? The last I heard a gallon was a gallon was a gallon if you get my drift. Did they want me to pay two dollars extra for the name on the milk carton ?