Passwords are secret and dynamic; fingerprints are public and permanent. If you don't tell anyone your password, no one will know what it is. If someone hacks your password, you can change it - as many times as you want. You can't change your fingerprints. You have only ten of them. And you leave them on everything you touch; they are definitely not a secret. What's more, a password doesn't uniquely identify its owner - a fingerprint does. Let me put it this way: if hackers get a hold of your thumbprint, they could use it to identify and impersonate you for the rest of your life.
I met the co-founder of this technology a week and a half ago. My understanding of the technology Apple paid $356M for is that it is more than simple fingerprint scanner. I believe the technology actually scans beneath the surface of the finger to make its key.
While not fail-safe technology, its not like a simple swipe of your fingerprint from a door handle will unlock the key. However, if that key is cracked somehow it does open up a pandora's box of exploitation.