That extra buffer is actually a very nice thing to have. First of all the Volt doesn't have a traditional starter motor and uses one of the motors to spin up the engine to start which requires sufficient remaining charge. If the battery were to go completely flat, you wouldn't be able to start the engine to keep going. Additionally it acts as a power reserve when the ICE can't provide enough power as your initial observation of 53kW output shows. Finally, one can think of it also as an emergency reserve in the event that you've depleted the initial charge and are running on engine power. If something were to happen to the engine to cause it to stop such as out of gas or even an engine failure, the Volt has the capability to use that very small remaining charge to maneuver the car to a safe location or to a gas station for a short distance, some have said as far as 2-3 miles. Personally I think having an extra 1-2 miles of range vs. the longer life of the main battery and use as a buffer and emergency backup makes more sense to have the latter. I sure wouldn't want to be caught out on the road only having engine power and trying to pass someone in a reduced power state once the battery has depleted.
Understanding Total Power gauge in gas mode
The gas engine generates maximum 53KW. When the battery is completely depleted (no electric range left) and the car demands access of 53KW then where does that additional power come from ? If it comes from the battery then why not power the car from the battery itself ? What am I missing ?
In the attached pictures you can see that the car is consuming 115KW and if the engine tops out at 53KW where does the extra 62KW come from ? If the battery is capable of providing that much power then why is the electric range 0, why doesn't it use the battery power until the battery can really no longer provide any power ?
