I understand the value of vermiculture, and grew up with a wormbox on the back patio that made beautiful castings. What I don't understand is the purpose of the bin.
If I kept a heap of worm-friendly scraps, mixed with some dirt and kept moist, and covered with a layer of dirt to keep pests away, wouldn't that accomplish basically the same thing as a worm bin?
In other words, wouldn't a poorly run compost heap that doesn't get hot basically turn into a worm heap anyway, no need for a bin?
I feel like I might be missing something important, but a heap is a lot cheaper and simpler than a bin, and wouldn't dry out as quickly or have as much susceptibility to temperature swings, and wouldn't rot and need replacing every few years.