So why are aircraft so often described as "private" when cars, boats and houses are not? It implies a distinction in the mind of the speaker.

An airliner is not public, it is as privately owned as your boat, just available for hire.

A corporation bus (if any still exist) is public. An RAF Tornado is publically owned, though not publically available. Many "private" aircraft are publically available for hire via a flying club, so why the distinction?

T'ain't logical!