I think you nailed it, the entire story and this part in particular. It is what I call "fractal redundancy" and I plan to write about it in terms of food, but basically it just means that every level (house, street, neighbourhood, district... and so on) tries to be as self-sustainable as possible. Shortages will happen and help is then provided along both dimensions; horizontally and vertically. It takes a strong community, but it can work.