Brian Thibodeau wrote:I'd be interested to know the reasoning/history behind this, but I see from that link that you don't know either.

Weird, but perhaps sources are out there . . .
Wikipedia offers this up, and a partial listing:
Many of these surnames derive from noble and official titles, professions, place names and other areas, to serve for a purpose. Some are originally non-Han, while others were created by joining two one-character family names. Only a few of these names (e.g. Ouyang, Shangguan, Sima, Situ) survive in modern times. Many clans eventually took on a single-character surname for various reasons. A small minority of Koreans and Vietnamese also have compound surnames.
http://en.wikipedia.org/wiki/Chinese_compound_surnameAnother site says that there are 81 compound surnames still existing in China.