Here's my rundown:
Cooking fires are not always possible: Think in the city, suburbs, living in an apartment, etc. You may not be able to have a cooking fire in an emergency due. Or you may not have a sustainable amount of wood, or your may not want the attention that smoke can bring.
Ease-of-Use: A decent propane stove is very easy to use and cook on. Turn gas on, light stove, begin cooking. The stove we have ran about $60 and has great adjust-ability, from roaring blast to a nice gentle simmer. It's clean, works like any other stove, and is just plain easy.
Transportable: Yes, you wouldn't want to go backpacking with one of these, but a stove and propane bottles is not a space-killer in a vehicle. Definitely worth bringing along if you need to bug out by vehicle.
Convenient fuel: Camping-stove sized propane bottles are everywhere and available for $2-$5 a piece. We've found these bottles last through more than a couple overnight camping trips without issue (cooking 2-3 meals per trip). With an adapter hose, you can also hook into larger propane tanks, which should last a good long while. Propane bottles are available all over the place and can be stored easily enough. They're easy to connect/disconnect, and there's no need to worry about spilling gas all over the place when refilling.
Affordable: Stoves are generally $50-$150 new, with deep discounts available if you buy used/garage sale items. Propane bottles are cheap, and you may already have a few big 'uns sitting around for a propane grill.
Dual fuel stoves
There you have it--the good old camping stove. Definitely a recommended piece of basic kit. I find many, many people that I talk to have some kind of food storage but zero plan for how to prepare that food in a grid-down scenario. Propane camping stoves provide an easily available, easy to use option for no-grid cooking.