Dear TRH – I know you wanted others' views…but… its me again! Thanks for the link to the pre-composting discussion – very informative! I'm sure my suggestion to Ms. Weeks to let the manure pile go several weeks would probably be overkill. At that point it would pretty much be compost and could be used as such. It wouldn't hurt the worms and would probably act as good bedding but there wouldn't be much nutritional value for the worms. As I said, I don't have any experience in traditional composting – and my vermicomposting operation is a very modest one.
You are correct; the main reason for pre-composting is to ensure that it will not get too hot for the worms. When you say "…pre-composting too much and killing off the beneficial bacteria.", I don't think that's too much of a concern. Rather, I think the concern is that the compost bacteria will have already consumed most of the nutrients. Really, what is going on in a large thermophilic compost pile, is that huge numbers of microorganisms are growing and breaking down most of the 'easy' to break down organic matter – the relatively simple carbohydrates, proteins and whatever fats may be present – and releasing lot's of heat in the process. This heat favors the growth of thermophilic ('heat-loving') bacteria that continue to break down the less easy organic matter (cellulose, pectins, and to some extent, lignins). What is left after complete composting is 'humus' which is more of this cellulose and lignin, that is only broken down very slowly. This is the soil amendment that slowly releases nutrients (nitrogen, phosphorous, potassium, etc.), improves soil structure and aids in moisture retention. Vermicompost is fairly similar, though studies have shown it can often be higher in these nutrients and may contain larger numbers of bacteria that can be beneficial for plant growth (just how much 'better' it is than regular compost depends on what you are feeding the worms).
The worms are deriving a large amount of their nutrition from eating the bacteria that are growing on the feed stock. The vermicompost pile is a mesophilic ('moderate temperature') ecosystem. That is one reason why the piles are not as deep as regular compost piles and that too much of the easy to breakdown organic matter is bad, as it will encourage the thermophilic bacteria. The idea is to strike a happy medium. Just enough 'easy to break down' organic material mixed with the 'harder to breakdown' material (paper, cardboard, coconut coir, shredded leaves, pre-composted manure, etc.), added in thin layers to the top of the worm bin, allows the mesophilic microorganisms to grow and breakdown the material. The worms do their part by keeping the pile well aerated, grazing on these bacteria, fungi and protozoa, as well as consuming any other easy to digest material (starches, proteins, fats) that the microorganisms don't get to first.