Many people drop (or should drop) the collision part of their own car insurance when the car is more than six years old. WHen this happens, they no longer have collision coverage for rental cars.
Credit card rental collision coverage gives a better benefit for those without collision coverage on their own car. Except for some Diners Club cards, your own collision insurance pays first (is primary) subjecting you to surcharges, etc. What is left, generally just the deductible, is picked up by the credit card company which provides secondary coverage.
If you don't have collision on your own car, your own insurance company, still primary, covers zero dollars and the credit card company, still secondary, covers what is left.
If you buy the (tremendously expensive and profit making) rental company collision, it is primary.
Disney hints:
http://members.aol.com/ajaynejr/disney.htm
>>> I wouldn't have to report it to my insurance company...
Incorrect. Always report all accidents no matter how slight.
>>> Which he IS my insurance company...
For those eavesdropping... not always. Most insurance agents are independent, representing several insurance companies.