>And a good counter to that is that a translation of a book into another language is still considered a derivation of the original work, not its own work, despite requiring a whole lot of creative human input on the part of the translator.

At the end of the day, it's all about legislation and case law--and judges making calls on the borderline cases, which creates new case law. It even plays into whether models themselves are copyrightable which, in turn, depends partly upon whether certain doctrines (like "sweat of the brow") apply under current copyright regime.