It was brought up recently that a couple of theme shops were selling commercial themes on both Theme Forest and WordPress.com. In light of recent GPL Drama, that caused some confusion about licensing allowances. StudioPress almost immediately took their themes off of Theme Forest, but Obox has not. Obox intends to sell with a 100% GPL license, but can't fulfill the requirements of WordPress.com's theme standards while still on Theme Forest. So, as Ian Stewart explains, they've been temporarily removed from the WordPress.com marketplace. Go read Ian's complete post on WordPress.com theme standards for more context.