I think what has to be considered here is how we view the future of the desktop vs. that of mobile. With the ever growing numbers in the mobile space along with tablets and other devices, I don't see desktops being as widely used/valued. Major companies are shifting their focus to these other devices which means more apps, which means more functionality, which means more possibilities, which means less need for desktops. So I think this is where the idea of "Design for Mobile First" is coming from.