Update: Matt Mullenweg has shared his thoughts with TNW:
The WordPress guidelines have been in place for years, before ThemeForest existed, and have served our community well as we’ve grown to power over 17% of the top million websites. Tens of thousands of companies respect the WordPress guidelines and sponsor WordCamps, including Microsoft, Google, and Adobe.
Hundreds of thousands of creators choose to license their work under the GPL, including everyone who has ever contributed to WordPress itself, we wish Envato would give their authors the ability to do the same rather than protecting their commercial interest under the guise of protecting their authors.
La WordPress foundation non permetterà più agli sviluppatori che vendono sul sito themeforest di partecipare ai WordCamp come speaker, organizzatori o sponsor dato che ThemeForest licenzia le opere con due licenze separate e questo, a detta della WordPress foundation va contro la GPL, licenza ocn la quale è rilasciato WordPress.
— Salvatore Laisa (@moebiusmania) January 24, 2013
Grazie a Salvatore per la segnalazione.