"fingerprint or pin" means that when the fingerprint scanner doesn't work, you can use the pin to unlock your phone. "fingerprint and pin" means that when the scanner stops working, you are locked out. Apple has obviously decided this is more of a risk/inconvenience than the extra security justifies.
I keep forgetting that this discussion is iPhone-focused. At this point, I'm thinking about other systems too, such as ATM number pads or entry pads for security gate/secure door systems. What if each button on the ATM was also a very fast fingerprint sensor? (What if the ATM had a cleaning device built in?)
