Actually, for commercial airliners its "worse". They require both a pilot and co-pilot behind the yoke, even in autopilot.
If an airliner is flown with less than two crew in the cockpit, even for a short period of time, the remaining pilot/co-pilot must wear a mask when flying above 25,000ft.
A friend mentioned that non-scheduled (no passengers or commercial freight) flights in large aircraft (eg. 737) can still operate with a single-pilot and a rated flight engineer only. The pilot had to have her mask on (or clipped to the helmet) for the entire flight. This option is rarely done commercially, obviously.
If an airliner is flown with less than two crew in the cockpit, even for a short period of time, the remaining pilot/co-pilot must wear a mask when flying above 25,000ft.