Actually it does...
While your last statement is true - that isn't really what matters.
Just because your local city contracts to the county or state for police enforcement - it does not change the laws the police can enforce or where the laws apply. What you highlight is simply an issue of jurisdiction. The real question is.. what laws apply.
The legality that matters is "can speed limits posted on private property be enforced under state traffic laws"
This is answered by the state law under 0316.640 (2)(a) State Uniform Traffic Control
(2) COUNTIES.—
(a) The sheriff’s office of each of the several counties of this state shall enforce all of the traffic laws of this state on all the streets and highways thereof and elsewhere throughout the county wherever the public has the right to travel by motor vehicle. In addition, the sheriff’s office may be required by the county to enforce the traffic laws of this state on any private or limited access road or roads over which the county has jurisdiction pursuant to a written agreement entered into under s. 316.006(3)(b).
The bolded part is the part of debate and where things are arguable about where the police can enforce the traffic laws by statute. It does not make the case black and white when it comes to a parking lot vs an access road in a lot, etc. Why? Those lots at Disney are behind access controlled gates. How can you argue the public has a right to travel on it, if it's restricted access?
But the last part, '...pursuant to a written agreement entered...' is probably what applies to most roads that would be Disney owned vs county. The agreement can not be just any 'please enforce the law for us' agreement, but an agreement that includes financial terms to offset the public's burden.
From 316.006(3)(b)
(b) A municipality may exercise jurisdiction over any private road or roads, or over any limited access road or roads owned or controlled by a special district, located within its boundaries if the municipality and party or parties owning or controlling such road or roads provide, by written agreement approved by the governing body of the municipality, for municipal traffic control jurisdiction over the road or roads encompassed by such agreement. Pursuant thereto:
1. Provision for reimbursement for actual costs of traffic control and enforcement and for liability insurance and indemnification by the party or parties, and such other terms as are mutually agreeable, may be included in such an agreement.
2. The exercise of jurisdiction provided for herein shall be in addition to jurisdictional authority presently exercised by municipalities under law, and nothing in this paragraph shall be construed to limit or remove any such jurisdictional authority. Such jurisdiction includes regulation of access to such road or roads by security devices or personnel.
3. Any such agreement may provide for the installation of multiparty stop signs by the parties controlling the roads covered by the agreement if a determination is made by such parties that the signage will enhance traffic safety. Multiparty stop signs must conform to the manual and specifications of the Department of Transportation; however, minimum traffic volumes may not be required for the installation of such signage. Enforcement for the signs shall be as provided in s.316.123.
4. The board of directors of a homeowners’ association as defined in chapter 720 may, by majority vote, elect to have state traffic laws enforced by local law enforcement agencies on private roads that are controlled by the association.
It is more than likely this type of arrangement that exists between DISNEY and the Counties when it comes to roads owned and maintained by Disney. (wouldn't be with Reedy Creek as they don't have any police to contract with)
Any county owned roads would already be covered by the county and county police would have the right to enforce traffic laws given the 0316.640 (2)(a) '...right to travel..'. Any roads owned by Reedy Creek would be public access anyway.. so again, already covered by the county.
If I were ticketed behind the toll plazas - I'd fight to ensure there was a legal agreement pursuant to the requirements above between Disney and the County that covered the parking lots because those are not open to public access.