Soda is actually free for Disney per their agreement with Coke.
Makes sense to me. The advertising value of having the coke logo plastered on the drink machines probably exceeds the value of the boxes of a syrup. If anything Disney could plaster a few more Coke logos around the park and charge Coke for the privilege.
Same thing for wine. Disney had a pretty sweet deal with Mondavi at California Adventure. I think the Mondavi were taking a loss on pouring their wines there and gave up. Probably the wrong demographic at the parks.