You in fact have shown that home roasting results in wood that "falls apart more easily". This says that the cellular structure has broken down. In the careful roasting in an oxygen-free environment with controlled humidity (as in the kiln drying process where water is injected into the kiln) you have far less cell damage. The wood is not burnt as you described, but undergoes a process called pyrolysis. There is a significant difference - burning produces carbon, pyrolysis doesn't carbonize the wood.