Having previously lived in Phoenix for several years, I can tell you that the amount of citrus on public property that falls to the ground and rots is huge. Even at high density apartment complexes, people don't pick near capacity (although this might have something to do with heavy use of herbicides on manicured lawns). There's no tragedy of the commons going on there (and I have to wonder if you've ever tasted a green orange)...

On the other hand, there are pretty sound reasons for planting edibles on public spaces instead of merely ornamental plants.