My gas furnace will not ignite without power and the power necessary to run the blower is 15 amps or so, wiring in a portable generator would be simple.
The water heater works without any power whatsoever.
The stove has electric ignition but you can light it without power. The oven needs power (I think? never tried it).
Gas is also often more reliable than electricity as gas is practically always buried while electricity has many overhead lines in the mix.
My water heater does, but the little recirculation pump on it doesn't so it takes longer to get hot water at a distant faucet.
My central heat does not.
Yes. The gas stove does not need any electricity, same for the gas water heater. It's nice to be able to cook and have hot water showers during blackouts.
The gas furnace does require electricity to run the fan, but it's not much. So running the furnace to heat the house during a blackout is easy to do with a small generator to power the fan while all the heating BTUs come from gas.
Here in PG&E land (might be the most expensive electricity in the country, but at least it's the most unreliable!) these are nice advantages.
It also seems like a bit of a weird reason to me as a big reason. But maybe you get a lot more power outages than I do. (I would imagine somewhere with a gas main, where gas heating can be economical, would not have very frequent or problematic blackouts. With no gas main, you use butane/propane which is not so economical). Plenty of people have camping stoves lying around which can be used in a pinch.