Hope he doesn’t say that. I’ve no love for them but the whole nature of the GPL as applied to projects is a contentious and far from clear area, and debates rumble on for ever and a day over the letter of the license.
I liked this follow up post about the GPL from the WP lead developer: http://markjaquith.wordpress.com/2010/07/17/why-wordpress-themes-are-derivative-of-wordpress/ I learned a lot about the license as well.
Yes it’s a pretty fair post, but note it’s not a conclusive treatise on the subject. It remains a damned awkward subject in many areas, good that he pointed out the possibility of split license to cover CSS / graphics if I create a graphic it remains mine unless I sign over the copyright on it same with photographers you may hire them to take a picture for you but they will retain copyright on that image for all eternity.