Welp... A lot of people still prefer dedicated gaming devices, even if most of their libraries are not exclusives. The success and popularity of the PS4 and Xbone seems to suggest that. Both Sony and Microsoft don't just offer these devices, but also invest in games and have their own studios. Their success, or at least their gaming devision's success drives and influences a large portion of the gaming industry.
Granted, not every studio needs to be in contact with Sony, Microsoft, Nintendo or even Sega and Atari to publish a game anymore, but The market being different from what it used to be decades ago doesn't necessarily mean doomz.
Even If they do shrink in a few years they would still be relevant.