Also - when you use your debit card with your PIN, that PIN has to be stored somewhere for batch processing (don't even get me started on why banking isn't real-time yet... see previous article). Herein lies the problem and the issue I am seeing with this VISA-demonstrated trend. Most people don't know to not use their debit card with their PIN... and to use it as a credit card. There is a massive difference in how things get processed, yes - but the main difference is your precious PIN.
Consider the role the compliance plays today, when a good chunk of people are still using their credit cards as forms of payment. Compliance is important because it causes you pain if you get your card information stolen and used... but ultimately it's not so bad because your money doesn't immediately disappear from, say, your bank account. If you start using your debit card plus PIN, and someone breaches a merchant you trusted with your information - your money disappears from your bank immediately. Are you ready for that? Sure, there is still the "Zero fraud liability" if you use VISA (for example) - but that's only if you use the card as a credit card.
There's a bigger picture when you zoom out from all the statistics and cost figures and trends of debit vs. credit. At the end of the day - if people start to use their card more as a debit card compliance (most notably PCI Compliance) goes from critical to possibly catastrophic!
Please, if you don't already know this... use your debit card as a credit card... avoid inputting your PIN at all cost. Tell your friends, family and anyone you care for.