No it doesn't apply to non-US flagged ships that sail in international waters. That was never part of the original complaint, and in truth US courts have no jurisdiction on foreign ships in international waters.
So for example it doesn?t apply to a RCI ship that sails the Mediterranean but it does apply to a RCI ship that sails the Caribbean and calls on a Florida port.
The only issue decided by the Supreme Court was "does Title III of the ADA apply to foreign-flagged cruise ships that call on US ports?".
The lower court will decide how the law will be applies - in other words it will decide what level of access vessels will be required to have.
I blogged about the decision today.
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Editor, Emerging Horizons
The only accessible travel magazine***edited to remover commercial reference***