[steventhedev]

You hit it on the head. IANAL, but I would argue that there are two good ways to go about arguing that a theme is not an infringing derivative work:

1. The parent class (more to the point, the interface which must be copied to be compatible as a theme) is not sufficiently specialized to be copyrightable in the first place.

2. Even if the code is derivative, the use and intent in copying is fair use because it was done to be compatible with the greater Wordpress system.

Sadly, because of the names involved (subclass, etc), I doubt that any judge without specific programming knowledge would rule that subclassing isn't automatically derivative.

My gut feeling is that those two idiots are on a collision course to sue each other. I'd say it'll be fun to watch the fireworks, but it's a bit hard to enjoy them when they're aimed at you.