Sure, those are different things. Maybe I misunderstood what the first comment was talking about, as I know of no system where you enter your debit card number to do anything.
This just highlights the fact that our global banking system works very differently in different parts of the world. And maybe, to close the cicle, as the article claims paypal really shouldn't forget this, as it has to behave differently outside of the US if it wants to stay successful. A different environment probably always needs a different strategy.
About the direct debt, sure, I can undo this, via internet banking.
But a fraudulent debt card purchase takes time to process and you don't have you money in the account anymore.
With a credit card I can check for fraud and my money is not gone if this happens (and yes, it has happened to me)