I find it a breathe of fresh air that their names contains their father's surname unlike most of the half-japanese characters found in other anime & manga series.
I can understand if the mother was the foreigner but why most half-japanese characters have japanese surnames even though their father was a foreigner?
I guess if you live in Japan its probably easier to have a Japanese surname. In fact Asians in america sometimes adopt more Americanized names. Though its usually a first name.