thanks for the feedback. Domestic policies have a number of benefits that include rental car excess (if you have an accident and have to pay a $2000 rental car insurance excess then you can claim this back etc), additional accommodation if not fit to fly home etc, cancellation expenses if something happens prior to your journey etc. For a cruise (even if domestic) usually medical expenses are not covered by Medicare, so we actually recommend you take the most basic international policy for a cruise which will then provide you with medical coverage on your trip.
Kind Regards, Cover-More Travel Insurance