Has this just come about because Delta debit cards now are called Visa debit cards?
I think the distinction between Debit and Credit is still there. Debit means you are asking a bank to immediately pay a debt for you. In doing so you acknowledge your obligations to settle the debt.
Credit cards imply you are asking a bank to lend you the means to pay for goods or services in advance. The Freedie Laker case established the bank in doing so carried some responsibility for the soundness of the transaction.
What spuds rightly draws to our attention is the bonus offer of a form of insurance against fraud now given by some banks for debit payments. Not to be sneezed at of course, but more limited in liability than credit cards.