In reply to Jimmy Smutek.

Seriously. Simple points. Can WordPress still operate without Thesis? Yes. Can Thesis operate without WordPress? No. Yet still you claim that Thesis is not dependent upon or in any way derivative of WordPress. It’s a WordPress theme.
Simple points, can Thesis and all other themes and plugins be made to function without WordPress? Yes. If so can it be considered a derivative? I would argue no. Unless actual core code and not just function calls has been used.
Your line of reasoning is that if a PHP file calls functions such as add_action, add_filter etc it is a derivative of WordPress. Does that sound right to you?