[fakedang]

Are you sure about that? Members of rich families in the US are routinely called as part of a clan - Roosevelt clan or Vanderbilt clan. Or they're collectively called something like Boston Brahmans.

It's less used in Europe, but they are still referred to as aristocratic clans.

[mbg721]

To me the connotation has always been something like Hatfields and McCoys, not exactly positive, but not linked to race.

[fakedang]

Brahmans isn't related to race either. It's just an alliteration. You're right that they are mostly referred to in the plural form (eg: The Roosevelts bought out....) but the clan usage is fairly common too (eg: he's a member of the Roosevelt clan/dynasty).