This type of direct access is fine on a console, but DirectX is primarily designed as an abstraction layer on top of arbitrary hardware. PC hardware isn't as predictable as the Xbox One, and yeah, it adds clock cycles. On PC you don't want to get that deep into the hardware: it has the potential to break compatibility, and because dev teams generally don't have the ability to test 5,000 different combinations of CPUs, GPUs and drivers, you try to keep as much compatibility as you can.