I am big time WordPress Enthusiast. The GPL announcement just came in front, read here.
In short For theme is just like “PHP in WordPress themes must be GPL, artwork and CSS may be but are not required.”

So now commercial GPL themes are official. I already decided to go with this. My company ARCom will work by GPL and we will convert all of our work in GPL pretty soon. Some Work might be under Commercial GPL too.

But issue comes with plugins development. As My Buddy Matt or WordPress said nothing about commercial Plugins.
Yes, plugins needs to be treated same as Themes, though me & my company mainly working on themes, but we did lots of work on Plugins and functionality. Most of the commercial Plugins are very complex. Themes are just the look, the front end. Plugins is the module that create various lovely functionality. We create those functionality with Plugin.
Matt understands all of it. We all love him. His understanding in finance is different, like the idea of enterprise Akismet. He love it in that way. Give everything free, if somebody need extended he could hire a developer or hire the creator. That’s why all GPL.

Some Related Post By Famous WordPress Lover

1. Matt Mullenweg, WordPress, GPL and why I think he really gets it. By Alister Cameron

2. On the GPL, Themes, Plugins & Free. By Joost de Valk

3. WordPress, StudioPress, The GPL License (Let’s Move On) By Brian Gardner

4. Getting Pretty Lonely By Daniel Jalkut