You also forget the fact that all the fossil fuel has been used up, cuz you know that was the whole reason the great war was fought.

You can't have a war over a resource that is no longer available though, so it would seem reasonable to assume that not ALL fossil fuels were used up, just that they were close to it and the war was fought for control of the remaining reserves.
But regardless, if there was no natural gas to use, I doubt people would have been using gas ovens before the war either, after all, gas ovens aren't much use without gas to use in them. So it would seem most reasonable to assume that either the ovens in the game are electric, or there was, at the time of the war, some form of fuel available for them to burn, whether fossil fuels or a synthetic substitute. A possibility which would seem to be supported by the occassional gas leak one can find in the game. But regardless, gas ovens still wouldn't be able to do anything unless they actually had access to said fuel, which would seem unlikely in buildings that have not been inhabited for over 200 years. But in the case of ovens in places like the Strip that already have access to electricity, it would seem reasonable to assume that they are still functional, especially since people in those places probably wouldn't leave them there to take up space if they didn't work.
But regardless, there already have been mods which include usable ovens, whether making all ovens function like camp fires or just specific ones. I doubt that the developers would include this in an update as those are generally to fix bugs, occassionally, they might adress aspects that weren't really designed so well, like fixing balance issues, as is the case with the changes to energy weapons in the latest patch ((I'm not really sure if the change actually did enough to fix the problem or not, though, but that's beside the point.) I'd say that ovens not being actually used for cooking, but just functioning as containers, is the way the developers intended it.