There is no regulatory requirement overall for an autothrottle. Boeing has obviously certificated airplanes for fail-passive autolanding without the autothrottle. However, the Lower Landing Minimum authorization in the US is done through the issuance of operations specifications, which are essentially regulations specifically tailored for that operator. Some programs have been approved premised on a functional autothrottle for all autolandings, whether fail-passive or fail-operational. So some operators may require this and some may not.