This is quite interesting. I lived in Okinawa for several years and remember how loathe they were to associate themselves with the Japanese Mainland "Honshu" - even calling themselves "Okinawan" and not Japanese with adamant fervor. A lot of that relates to World War II era atrocities committed on the island, but, regardless, I think Okinawans see themselves as largely very different from the mainland Japanese even though they are citizens of the same country. That would be yet another distinction that I think this article sort of missed as it only referenced differences between far north and the rest of Japan.

Having lived in both mainland and Okinawa, the cultures are rather starkly different as well - Okinawa with a pretty typical, more laid back island culture and mainland with a bustling, busy one. In this regard, Japan isn't as homogeneous - both culturally and genetically - as the article would have you believe if the covered area were to include Japan's southernmost islands.