Gotcha...and I just doubled checked
the Apple site--it is indeed required for Touch ID users:
Notes:
If you have trouble enrolling one finger, try enrolling a different finger.
As you use Touch ID, it will continue to learn and improve recognition of your fingerprint.
Using Touch ID sets your Require Passcode setting to Immediately. You still have the option of entering your passcode simply by sliding to unlock.
If you unintentionally slide and reach the passcode entry screen, you can still use Touch ID to unlock your iPhone (as long as there haven't been five unsuccessful attempts to recognize your finger).
Touch ID works only for fingers that you have enrolled. You can enroll up to five fingers using Settings > General > Passcode & Fingerprint > Fingerprints.
With each additional finger that you enroll, it may take slightly longer for Touch ID to recognize your finger when you use it.