The guidebook is wrong.
The southernmost point of Japan has exactly that "end-of-the-world" feeling to it, that makes it an adventure to visit.
True, the rest of the island is mostly sugarcane fields - but the south coast is made of barren volcanic cliffs constantly hammered by ferocious waves. The cliffs, however, stand firm - and the fields are well protected.
Thus, Hateruma-Jima becomes to me a symbol of how Japan has been able to protect its culture from foreign influences.
On our 3500 km travels from Soya Misaki in the north to Hateruma-Jima in the south, we have come to love the people and nature of Japan. We know that we have only scratched the surface of the culture, but everywhere we have been allowed to peak through, we have discovered a sophisticated and self contained culture and philosophical basis very different from our own.
I am sure that one reason for the great difference is that christianity has not had much influence here. After initial missionary work by Portuguese and Spainards in the 14-15th century, christianity was outlawed for 300 years - and today only 1% of japanese are christians. Thus the philosophy inherent in christianity has not affected japanese thinking very much.
Another reason is the richness of Japan: the islands have been able to feed a very large population - and it has been self sufficient in almost all areas - limiting trade mainly to luxuries. The large population has enabled cultural growth.
Today, Japan is obviously interacting more and more with the rest of the world. But it will remain a jewel of uniqueness to the visitor for a long time. The jewel is encased in an oyster shell and somewhat difficult to open - but worth the effort.