How the card's authorized has nothing to do with the payment method. It is totally possible for transactions to be authorized offline contactless and submitted at a later date, for instance.
My understanding is the United States has a zero floor limit now, as a consequence of Dodd-Frank. Because you can make the bank deny overdrafts caused by debit cards, and due to the prevalence of prepaid cards, the merchant must perform an authorization with the transaction amount or else they will be liable if the transaction doesn't settle. Only very specific merchants, like transit systems, are exempt.