Charles,
I have to agree with you that the type of frame you describe will have a lot of sway. I wonder if the infill material in a trditional Japanese frame is what provides the lateral stability. Other than full scale testing of actual joints, I do not know of any calculations that will yield meaning full numbers on the rigidity and strength of the frame you describe. In the 1995 earthquake that hit the city of Kobe, many of the deaths were the result of the collapse of traditionally built residences with heavy tile roofs. Many new western style homes (stick-framed w/ plywood) in the region suffered little or no damage. Somewhere in the evolution of traditional japanese housing there was an ommission in seismic resistance. Perhaps the events were few and far between.
I would recommend braces or plwood/SIPS to resist racking. When all else fails, there is always steel.