I agree that the poster only has a superficial understanding of the GPL. Interestingly in the case of Wordpress themes the Software Freedom Law Center has argue

I agree that the poster only has a superficial understanding of the GPL. Interestingly in the case of Wordpress themes the Software Freedom Law Center has argued that these are derivative works, even though one could argue that these merely use a API cf http://wordpress.org/news/2009/07/themes-are-gpl-too/ http://wordpress.org/news/2009/07/themes-are-gpl-too/