I agree with Brian's method of differentiation. I'm also inclined to believe that the incorporation of metal fasteners may parallel the developement of codes, engineering standards and plan reviews. Wooden joinery is very difficult to analize, due to the anisotropic properties of the basic components in the system (wood).

This problem still affects timber structures in ways that urk even the casual entusiast. For instance, timber frame bridges that have survived for over a century as true wooden trusses cannot be repaired without the addition of steel to "strengthen" the connections. Unfortunately this "improvement" invariably shortens the life of the truss, due to the incompatability of the materials, which is multiplied in an outdoor environment.

In a nutshell, timber framed vs post and beam is a classic example of you get what you pay for. Unfortunately, some customers don't realize they are paying for one, and getting the other.