@Jacob Santos -
products dependent on the software must also be GPL

GPL covers "derived from" NOT "dependent upon", which is where this entire mess starts.

@Chip Bennet -

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.

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.

Your analogy here is worse than the Firefox/Linux analogy. Thesis isn't WordPress re-wrapped and bundled as a separate application, as in the case of a Linux distribution derived from Ubuntu.