@redwall_hp -

I still don’t buy-in to the derivative works argument. WordPress is a self-proclaimed “platform.” Linux is a platform, Mac OS X is a platform. Writing an application that runs on Linux doesn’t mean the application has to have a GPL license. Firefox runs on Linux, but that shouldn’t mean it should have to be licensed under the GPL.

The Linux-Firefox analogy is completely non sequitur, and in no way applies to WordPress and WordPress themes.

A better example would be Ubuntu and its various derivatives. A non-GPL package can run on either distro, but because Ubuntu is GPLed, so too must any of its derivatives be GPLed.

Remember the definition of "derivative work":

A “derivative work” is a work based upon one or more preexisting works, such as a translation, musical arrangement, dramatization, fictionalization, motion picture version, sound recording, art reproduction, abridgment, condensation, or any other form in which a work may be recast, transformed, or adapted. A work consisting of editorial revisions, annotations, elaborations, or other modifications, which, as a whole, represent an original work of authorship, is a “derivative work”.

Firefox isn't an editorial revision of, annotation to, elaboration upon, or other modification of Linux. Firefox doesn't depend upon Linux to exist or to run. It clearly isn't a derivative work of Linux.

Ubuntu Netbook Remix, on the other hand, clearly is a derivative work of Ubuntu.

I'm curious how you could argue that a WordPress back-end admin UI interface written for a theme isn't a derivative work.

(On the other hand, it seems pretty clear to me that a CSS file, for example, is certainly not a derivative work.)