I can assure you I am VERY familiar with how things work at WDW and RCID. I have had the opportunity to work with and talk with employees from just about every department of RCID, I have visited almost all RCID facilities, I have worked with and talked with Bay Lake Ct. residents and Disney executives. While RCID is often portrayed as just a formality to allow Disney to do extra things they are indeed a legal public government and are held to the same standards as any other public government. They work well with Disney but absolutely operate separately.
As this relates to the topic at hand RCID purchased the land from Disney and is constructing the parking garages and will operate and maintain them over their lifetime. Disney is not paying anything at all directly for the garages. The garages are public property meaning the public has a right to use them, in other words even if WDW trespasses someone from WDW property they will still have a right to park in the garages. The garages at Universal were paid for and built by Universal they are their garages. The reason this would be an issue at HS is it is a gated theme park and is restricted to only paying guests. A parking garage there would not serve the general public and it would be far more difficult for RCID to justify spending tax dollars to construct it. If a garage was built at HS Disney would have to pay for it and build it.