I agree. Fallout 3 also made no sense that everyone was STILL mostly eating only pre-war food. I mean, its been forever, it took place, timeline wise, after fallout 2, yet there was no advancement of infrastructure. It was like the bombs dropped 5 years ago.
I imagine pre-war food will be very scarce, but probably at this point in the post-apocalyptic world, food isn't a huge problem. NCR is very well-developed and have many cities and a large population. Check out the fallout wiki about them - they are huge. I imagine there are huge brahmin farms and crops (like you could find in Fallout 2, Modoc is one example)
By this token no firearm/energy-based weaponry/missile launcher type weapon should exist in game (or at least be usable). In fact, Hoover Dam should be not producing electricity anymore due to no more equipment being produced (after 200 years, you should be out of spares), all buildings should have collapsed, etc.
Point being, if you are going to complain about the abundance of pre-war food, you have to do the same for the use of pre-war weaponry 200 years after the bombs fell, along with other things.