I agree that the real issue is whether "you pay for the entire rental transaction with your eligible MasterCard card." See:

http://www.mastercard.com/us/persona...y/index.html#9

Of course those aren't the full disclosures, so who knows what the language is in the actual T&Cs. But I've always been under the impression that unless the charge on your card (for the full amount) comes directly from the rental agency or common carrier (airline, train company, etc.), your credit card CDW and travel/lost luggage/cancelation benefits do NOT apply. This is why I don't reserve cars with Priceline unless they're MUCH cheaper than renting directly from the rental agencies, and why I try to use vouchers I get all-at-once rather than spread out over various car rentals/tickets.