This template is licensed under a Creative Commons Attribution 2.5 License. This means that you are free to use and modify it for any purpose, but you must include the provided link back to my website. I have agreed to let users remove the link for a fee of $20. Removing the link (not paid for) is the same as breaking the law and action can be taken against you.

This of course, flies in the face of the GPL license that Wordpress itself ships with:

You must cause any work that you distribute or publish, that in whole or in part contains or is derived from the Program or any part thereof, to be licensed as a whole at no charge to all third parties under the terms of this License.

If that wasn’t clear enough, GNU explains that “modules [that] are designed to run linked together” constitute combined code. So, any theme, plugin, extension, or hack currently existing that I know about which uses the Wordpress API falls under the GPL license. The key point for this is that Wordpress does not include a special exception for themes. Matt Mullenweg (the creator of WP) hit the nail on the head in a forum thread:

Themes link and use lots of internal WordPress functions, which make them linked under the GPL and subject to being a GPL-compatible license.

If a theme (or a plugin) used no internal WP functions or APIs, then it could probably be considered independent, but that would be really really hard for a theme.

For more about Sponsored Links and Wordpress Themes, check out:

• Switching from Creative Commons to GPL
• The WordPress themes debate
• “Sponsored” Themes
• “Sponsored” Wordpress Themes
• Deteriorating Community

Update:

In a new post on the Wordpress blog, Themes are GPL, too, Matt Mullenweg speaks out to clarify the themes as GPL discussion:

Specifically, the CSS files and material contained in the images directory of the “default” theme are works separate from the WordPress code. On the other hand, the PHP and HTML code that is intermingled with and operated on by PHP the code derives from the WordPress code.