Since VB is not located at WDW, they probably have a different mug and a diferent policy/price for the mug. If I recall, you can only refill the mugs at the pool. Not a benefit if you are out on the beach.
DVC resorts have larger refrigerators than the non-DVC resorts, so it's usually a lot easier to just fill up your refrigerator with your favorites and skip the mug.