You are describing an emergency scenario. Everyone should be prepared for emergencies but I don't think having a gas furnace or stove should be part of that plan. Using them during a power outage can be extremely dangerous.
The advantage is that there is no grid dependency. People in Texas also lost gas during the blackouts because it was quite limited also used for electrical generation. It wouldn't surprise me if an earthquake could upset gas infrastructure in the bay area. Or some other disaster.
And with no power, you may not be venting. Sure you know to open a window, but every year people die from not opening the window.