Chick_magnet, I have the same question. When I was growing up my mom kept chickens, and she didn't buy them commercial food. They free ranged over our property and we always had eggs. I never remember one dying of starvation. I'm sure we would have gotten more eggs if we would have fed them commercial food, but so what? We got all the eggs we needed, plus some to sell, and the chickens seemed "happy" chasing bugs, eating whatever food the cats left behind, and scratching around in the dirt. I don't know what mom did with the chickens in the winter, but I'll ask my dad if he remembers. I also have an Amish neighbor who has a large quantity of chickens, and he doesn't feed them in the summer--just the winter.
I, too, am toying with the idea of just letting my hens free range and see what happens. I used to give them all the feed they wanted, but now I just give them feed in the morning and have them fend for themselves the rest of the day. If you decide to try "free range only" please post and let me know how it goes. Good luck to you!