They are partly GPL.
What the Dev Blog’s post (WordPress Themes are GPL Too) glossed over is that only part of a WordPress theme is required to fall under GPL/compatible licensing.
Here’s a plain English translation:
What that missive fails to understand is that most designers don’t necessarily give too much of a hoot about the underlying PHP code, it’s the graphics and styling.
In some cases, I’ve done WP themes that use hand drawn sketches that have taken me days to render and color. Unfortunately, there will be too many people who just read the post’s title without actually reading the content and will think they have a claim to that hard work to do with it as they please because it’s automatically part of the GPL. Here’s the kicker, it’s not. It’s not GPL unless the creator says so. In fact, it may end up being copyright infringement.
Think about a theme that was ported from a different system that uses another designer’s artwork. It’s uploaded to the WP theme viewer. People are going to assume the artwork is GPL too since, during the port over to WordPress, the original license terms were blurred. What happens when the original creator of the artwork begins policing it?
Plus, the woefully unclear Dev Blog post might mean more designers stop designing for WP once they realize their artwork may be at the mercy of GPL. Or even because of the threat of others not understanding that their artwork is licensed differently than the underlying theme files.
Will it work? Maybe, maybe not. Only time will answer that question. But it would be considerably difficult since WordPress.org will only support theme developers who release everything, including images/CSS, under the GPL or compatible license and not every designer is comfortable with that. There are some who are willing, but without fresh new ideas, those designs (because every designer has his/her own personal style) will get very stale very fast.
Overall, I believe this whole discussion which has been trampled nearly to death is about one thing, and one thing only: respect. Designers would just like to have a bit of respect for their work. It’s the same with plugin developers and even WP volunteers. People should extend the same courtesy and respect they expect for themselves to others, and we wouldn’t be in this mess at all. Unfortunately, that’s called Utopia and it doesn’t exist.
(By the way, since most people don’t seem to know this, WordPress is GPL because it’s a derivative of b2.)
Getting Pretty Lonely: an excellent essay explaining why the GPL license may be detrimental to commercial developers.
gifts: a very insightful comment by WordPress Wank that somehow disappeared from Lloyd’s post on themes being GPL.