I disagree. During an autoland the RETARD callout at 10'RA is very much a command. The thrust should have already started to reduce to idle from around 30'RA and IDLE should annunciate on the FMA from 30'RA. Think about a CATIIIB autoland with no DH (no visual references required), you have no visual cue when to retard. It is a totally automated approach and the system is telling you when to retard in preparation for the autobraking following touchdown
Some confusion can exist when executing a non-autoland (manual) landing without both autopilots engaged. Here the RETARD call is at 20'RA and is more of a reminder and not a command. Depending on your speed they may have already been brought back to idle as this prompt is made.
During autoland if the THR LVRS are not brought back the aircraft will land just fine and at idle thrust, but as Henry VIII says with no spoilers and therefore no autobrakes. Manual braking without spoilers would work OK although I would never want to try this theory.