If any portion of Thesis is derived from WordPress (WP functions), the whole of it (WP functions + extensions) is GPL because it's a combined single program.

And if it's GPL, then the GPL license is granted from the original (WordPress) and not from Thesis. Now, infringing on CSS, TM and/or images is different, but I don't think Chris has a case for infringement on code, as the licensed code doesn't originate with him.

But it looks like this is a case of style cloning, not code copying. In which case, Chris is a douche, but it has nothing to do with the GPL. Any theme explicitly attempting to copy the "look and feel" of popular news sites or of sites like facebook, twitter or is probably violating copyright if not TM.

[P.S. You can get protection (copyright, TM, etc.) on "look and feel". It's more established and understood in copyright law then anything related to css/html or code. I believe the measure is you can't make something look so like a competitor as to cause a potential misidentification. Something so generic as a framework though shouldn't fall under this.]

I find myself agreeing almost entirely with Chip for a change :), but if the output matches exactly, and the code different, see "look n feel" infringement above.)