kevin, of course you are right.
h/e there are some rental places that will either place a hold on a LARGE amount of money in your account for up to 14 days, (even after you've checked out or returned the car) OR will not take a debit card. (yes it does happen)
also, you are not offered the quite the same protections with your debit card as you are with credit cards in the event of fraud. and if you pay in full every month, why not enjoy the benefits of a credit card?