News Flash, the PC industry is shrinking. Even Intel are struggling to keep up sales of their CPU's.
Its not what it once was, less people are spending large amounts of money on hardware to play games, and who can blame them when all they read in places like this is that the only option they have is to buy a Motherboard and CPU which alone costs as much as a PS4, and then the rest on top of that...
And it will only get worse unless PC Gaming can be more affordable.
News Flash, PC gaming has already gotten cheaper. AMD has introduced a number of APU's that run most games at 720p with decent options. You will find many of the PS4 titles only run 720p as well. You can easily spend 400 or less and put together a PC quite capable of gaming and more.
The market shrink is not necessarily what it looks like at first glance, you have to take into account quite a few things.
1) Many people who previously did not have a modern pc have already bought one, so the number of people who can be targeted as new customers has shrunk
2) Tablets, phablets, super phones, streaming boxes, and wearable technology will eat into the PC space somewhat but were not the target of discreet GPU's
3) As Tablets etc remove from the PC market they will mostly remove from the low end of the market, the new low end PC market is quickly becoming capable of gaming with APU's and no discreet GPU necessary. This cuts into GPU numbers a bit.
If steambox takes off it may help to reinvigorate mid and high end gpu sales.
Cheers!