[BobbyH]

In addition, if I purchased the Thesis theme, although the GPL would give me the right to redistribute it, I would not be able to market my redistributed theme as "Thesis", presuming that Chris has trademarked that mark.

So if I tried to redistribute the theme as "Thesis", Chris could (1) sue me for trademark infringement. He could also (2) file a DMCA claim against me (or sue me for violating his copyright), if my product included his copyrighted CSS/JS/images/etc.

These remaining trademark and copyright protections are why Matt asserts that applying the GPL license to the Thesis theme would not hurt Chris' business.