On the old system, you can't do a debit transaction at all. It has to be credit.Why can't you just swipe the card on that device and enter your pin number on it?? Doesn't make 1 bit of sense. Kind of makes using it pointlessw if you have to go to ANOTHER terminal.
Debit transactions contain the users PIN, obviously. When you swipe the card, the swiper has to immediately encrypt the users PIN before it sends it off to be authorized. The encryption used is specific to (and injected into the swipers by) the credit card processor that Apple uses.
I'm guessing that they either don't want to do that piece, or the touch isn't capable of doing that piece.
Either way, it's at least offering a feature that can't be done in the Apple Store now (which is use a debit card + PIN with an EasyPay), even if it's not being done in the most convenient way.