And that's the benefit of something like TouchID. Since you rarely have to enter your full password (after restart or too many TouchID failures) it's much easier to use a longer or more complex password than 4 digits. Even a simple dictionary attack would take a very long time at one attempt every 40s.
Well, I'll say I don't have to punch in my 4 digit PIN much, perhaps that's what you meant. But the 'full password' - the Apple ID password - I have to put that in all the time. The touchID verification for apple store downloads seems to only hold for an hour or so, then I gotta punch in the full painful password again... :(
That happens if you turn off your device. There might be a setting or option you might need to enable. After I've restarted, I enter the password once in the store, and after that, touch ID works.
72 hours is crazy - do they expect people to be buying stuff all the time?
What's crappy about it is that they force a moderately complex password strength which is much harder to input on a touch screen keyboard. I'm constantly having to enter that - the 'touch id' for using the apple store, to me, is effectively uselesss. For unlocking the device, it's fine.