We have always had refills for our drinks. Sometimes we don't even ask and they just bring another one. We have not been charged for refills at any TS restaurants.
Usually the restaurants in the Theme Parks, Resorts and DTD should have refills on drinks. When it comes to the counter service locations if the Cast Members get the drinks for you then there are no refills, however if you get the drinks yourself then there are refills.
Well, on alcohol, no they don't. Sure would be nice if they did!
My husband and I like to get the flavored sodas at table service places (like the cherry Sprite at 50s Prime Time call Mickey's Bee-Bop). They will even refill those for free (and I got a "to go" cup with the Mickey's Bee-Bop in case I was thirsty later).
Except for the Electric Umbrella at Epcot, there are no free refills at the counter service places.
Free refills on coke/tea/water at all TS. No free refills on smoothies, alcohol or milk. However we did have a waiter at Chefs de France who said you could not get any refills on soda with the dining plan (not sure what was up with that and in ten years this was the ONLY time I was ever told that).
No free refills on CS unless you get the beverages yourself (food courts).
Ah, have you seen the price of milk lately? Can you blame them? Milk is much more expensive than fountain drinks, ice tea, coffee etc. Besides it is usually so hot there I wouldn't want that much milk on the tummy.
Our last trip, Sept. 07, at Coral Reef, they were strict about no free refills. This was the only restaurant we encountered on the DDP that enforced no free refillls. All other restaurants were plenty of refills, no extra charge. It probably depends on the cast member serving you. Over the years, as consistent with service that WDW is, we have noticed minor things like refills varying. Nothing that takes away from our trip.