To the bark versus wood question, yes, there is a big difference. They are completely different kinds of cells produced for completely different purposes. A simplified version of there positions:
http://www.appleman.ca/korchar...
In virtually all woody plants, the bark is more resistant to break down. It's natural purpose is to defend against environmental stresses and pathogenic invasion.
In the end, is one better than the other for a growing medium? I don't know. Certainly, individual characteristics would vary depending on the species of wood or bark used, and how they are produced. For example, wood chips would have different properties than shredded wood.
... cypress wood is rot resistant and might last many times what Douglas fir bark lasts. Good or bad?
Don't know the answer to that either. But it has been shown that some resins/chemicals (in some trees) responsible for rot resistance has been deleterious to growth of certain plants. So who knows?
