"Why would Shimano have done an English language service manual for the SG-8R20 and never have apparently updated it for the later hubs?[/quote]"
Purely mechanical reasons: It didn't fly off the presses and sell out.
Regards social paradigms and the difference between German and Japanese hubs: Germans live among houses that are over 1,000 years old. The Japanese are used to living in houses made of paper.