Obviously, the rumor sparked speculation regarding a potential collaboration between Apple and the game publisher.
Valve is a video game firm producing successful titles for PC and console, but it is especially known for holding Steam, a sort of iTunes Store dedicated to computer games.
Over 1400 games are currently available to an audience that is around 30 million active users.
The platform was launched for Mac in May 2010 and gradually emerges as a true gaming portal.
Valve has recently launched a companion app for iOS, which lets you view the latest news, but also browse and pay for games you can then download to your Mac or PC.
At the moment there is no clear reason for Tim Cook’s visit, but many view it as the beginning of an extensive cooperation on several fronts that could eventually lead to the integration of Valve directly into the iOS.