Board Thread:Speculation House/@comment-10390252-20130728185452/@comment-4830106-20131114044709

Or maybe it's just out of habit that they go by different names. For example, Cersei is technically a Baratheon by marriage, but everyone calls her Cersei Lannister anyway.

I'm not sure how that would work for Ruby and Yang (since neither of them are married), but just a thought.