Worst case scenario...major earthquake, all gas and water lines broken and leaking, power lines down.....you have no power. Still want natural gas?
With diesel, you can store hundreds of gallons(even thousands if you have the space and money) of fuel, stabilized for up to fifteen years. Fuel is on site, less volitile than gasoline, more versitile than natural gas, replentishable, rotateable, useful as heating fuel or motor fuel for vehicles. Could also be sold or bartered if need be.
Just a note: Any shelter designated as a fallout shelter must have its own emergency power supply, comletely independent of outside utilities. Not that your home is a "fallout shelter" but the reasoning behind the requirement is sound. Utilities go down under bad conditions....self containment is key.
Dependence on a utility means you are at the mercy of their abilities to maintain service in a worst case scenario. Personally, that is ultimately when I want to be completely power independent.
Just my 2 cents.......derived from experience in the generator maintainance and retrofit field with a major Boston area company.