The essential difference is that a hold can be placed on a credit card and the credit card company (Visa) takes the responsibility. On a debit card there is no guaranteed hold.

Why? Say you go into Hertz in the morning and that $1000 hold gets placed on your debit card. Then checks that you wrote last week arrive at the bank. Do you want the bank to return those checks because Hertz put a hold on your account? (Remember, Hertz will almost never debit your checking account for the full amount of the hold.) Even if you have a draft facility (overdraft line) on your checking account, Visa has no way to monitor its availablility.Once Hertz has experience with a customer it will accept a debit card (and not place a hold).