@iMadalin - I'm not sure how your comment has relevance. Nobody is disputing the relevance of the GPL nor is anyone discussing if WordPress themes and plugins are considered derivative works. I'm not sure you quite understand what is being discussed here. The GPL does not prevent you from selling GPL products. In fact they encourage it.

I strongly suggest you read this:

http://www.gnu.org/philosophy/selling.html

This is a direct quote from the GNU project from that page. The people that wrote the GPL:

"Many people believe that the spirit of the GNU Project is that you should not charge money for distributing copies of software, or that you should charge as little as possible — just enough to cover the cost. This is a misunderstanding.

Actually, we encourage people who redistribute free software to charge as much as they wish or can."

So again, I don't see how your comment has any relevancy to the discussion at hand.

But then again, far too many are not educated on what exactly the GPL is and isn't. People make false assumptions. Educate yourself and then joint he conversation.