Many rental cars are leased fleets. They are returned to the manufacturers when the leases are up. They do need to repair the damages in order to get back the residual value.
Regarding the poster's comment about he can dispute the loss of usage claim put on his card, I would like to point this out that yes, he can, and credit card could possibly cite with him and charge back the rental car company. However, the rental car company can still go after you, by assigning your account to collection agency, as you do sign the rental car contract and are responsible for damage to the car since you decline the insurance. To us, a couple hundreds are not worth the hassle to deal with a collection agency, especially there is a potential the unpaid claim could go on the credit report. Then it is a lot more hassle to clear it up.
In our hail-damaged car, there were about 35 to 40 dings on the car top and the rear cover - it seemed the storm was blowing from the rear and the front of the car was protected somewhat by the body itself. It would take at least 3 to 4 days in total time to repair those dings and repaint the car. (there are time required between prep and paint, and may be more than one coat of paint). When we took the car at JAC, walk-up customers did not get any car - every rental company was out of cars - so we felt the loss of usage claim was legit, although of course they charged the full rate without any discount applied - and we all know that nobody rent a car without any kind of discount code... Well, may be there are still some folks do so, judging by those walk-up customers at the JAC counters...
Visa covers Admin fee up to certain amount (forgot). MC does not cover Admin fee.
Dont know about Diner. But AMEX has same exclusion list as MC. Last time I looked, other than New Zealand, The rest of countries are excluded by Visa as well.
However, since New Zealand is a no-fault and the renter is compulsory taking out basic LDW (included in the rental rate), you would need to have a letter from the rental car company to verify that you cannot voluntarily decline LDW, in order to satisfy Visa. Further more, when renting in NZ, the law allows the rental company to IMMEDIATELY CHARGE your card for the NZ 3000 and up "excess" (deductible) on the insurance. Such "excess" is refundable when you return the car without any damage / scratch / blown tires/ windshield breakage (actually I think Windshield is a separate insurance item). Whether you want to have such a charge put on your card no matter what, and try to make sure it is credited back when you return the car at the airport, is a personal choice. In our 3 trips to New Zealand, our experiences are, given the weather and road conditions, you will bound to have some dings and scratches no matter how careful you drive. At NZ22 a day for a Corolla, you can reduce the "excess" to NZ300 - so again it is a personal choice whether you want to buy the extra insurance. At current exchange rate, 1 NZD = 0.60 USD - that is a lot cheaper than the USD25 per day insurance in Florida!
The alternative is to rent much older cars from locally owned rental car companies - the cars generally are between 5 to 10 years old. If I am driving in South Island, I would definitely not to take such chance. You can be stranded in somewhere when your clunker died, and it may take days before you can get another car - the services usually are contracted to NZ AA and you can imagine that is not the fastest service.