Some people are making fun about this, but if you look at the history of the steam store and how Gabe is focusing so heavily on Linux, it is because he is concerned that Microsoft is going to shut down Win32 and he will be absolutely screwed.
Due to this, he is creating a safety net for himself and is pushing Linux hard as an alternative to Microsoft Windows so that he can not be so reliant on Microsoft and what they choose to do and not do. Specifically when it comes to win 32.