Special thanks to Mixergy for sharing this video with WordPress.tv.
October 17, 2009 — Hiromichi Koga’s presentation “Megumi GPL / Commercial Theme” at WordCamp Kyoto 2009 in Japan.
「め組テーマ (GPLとcommercialテーマ)」 小賀浩通氏講演 ワードキャンプ京都2009 （日本語音声）
Video by Hiro Shinohara & Ian Cheung (Messaliberty).
October 13, 2009 — Matt Mullenweg gives an overview of the GPL and how it benefits WordPress, why WordPress is licensed under the GPL, how the GPL fosters innovation, affects themes and plugins, and creates value.
The directory of premium theme authors who support the GPL as mentioned in the interview is located here.