Yeah, that was pretty much my thinking. I do agree that there could definitely be situations where "adopted" wouldn't do that. (Sort of like why I am for stories about blended families happening when the children are older, and the step-siblings turning out to be into each other, or a situation like the Cohens and Ryan Atwood in The OC, where he's part of the family but not, so there would be room there for Seth/Ryan if that's a route they wanted to go.)