Oh yeah makes sense as the hybrid depends on the motor to drive all the time. Logic would make sense that if you had a full HVB you should be able to drive while out of gas, as if it happened while the engine was running and the car said stop safely now and you did and power cycled it back on in Auto mode you would expect that it would use the battery first before looking at the engine again.
If the battery died you could still plug in the car and recharge the HVB normally to have enough power to start the engine later. I see no difference in this as you should be able to recharge you HVB even if it was dead (0%) with the stock charger or a HV charger as the 12v battery should still be good to throw the relays to charge up. Only if the 12v battery is dead then the car is disabled (even with a full HVB) as you can't click the relays to charge up the 12v battery or to power on the car to drive it and charge the 12v battery while in motion from the HVB.