Yes, most of that land is going to be parking and roads, although it may turn out to be a garage instead of a surface lot.
They actually bought 3000 acres in southern Osceola and have applied that towards an additional 350 acres of wetland impacts, a process that took well over a year of back and forth with the SFWMD. As you said Disney does built on wetlands sometime, but recently they have been trying to avoid it. A good example is the new laundry facility where they had the access road take a roundabout path to avoid wetlands instead of build the road straight through them. They also adjusted the Wilderness Lodge DVC expansion to reduce the amount of wetland impacts they were going to have.
Yes, obviously Disney can change things, but they don't have 100% control of the board, they are answerable to outside agencies. The suitability rating and wetland designations aren't just colors on a map, there are real difficulties involved when they want to build on wetlands. There is a lot of extra permitting and engineering involved.