It's easier for developers to create multi-platform games if the hardware is based on the same architecture.
Sony: Developers Requested x86 Architecture for PS4 : Read more
Sony: Developers Requested x86 Architecture for PS4 : Read more
Regardless the hardware, it's the software that counts. Consoles will still have exclusive. SONY/MS/Ninterndo will make sure of that, regardless if it's the same PC hardware inside. Furthermore, next gen consoles will bring features like better motion detection (Kinect 2). And this is not supported on a mass market yet on the PC.