The end result may be the same, but the process matters, and the credit card protection is stronger. These debit card protections are marketing ploys, not legal rights like those which protect credit card users. During the time that the bank investigates unauthorized transactions I would rather have my credit line impaired than my bank account balance.
For what it's worth, the 2 times in the past year that I had to file a dispute on a business debit card, our bank initiated a credit for the funds immediately. There was no "impairment" on the bank account. Perhaps that's not universally the case. I'll just say that while Amex has always been really good, honestly, my experience has been that it's FAR easier to work with the bank we have a relationship with (and which quantifies our business not in terms of a credit line/history, but in terms of actual deposits/assets) than with any credit card company.