Whatever is going on, they look absolutely [censored].
I plan on getting into game development, specifically graphics side. But heres an explanation.
Real time shadow mapping is impossible due to the way that shadow mapping is done. What basically has to happen is that you need to do some math for each and every pixel on screen. Now if you did that on the CPU you would be doing that one pixel at a time. In the case of GPUs you have things called stream processors which basically do this as well, except you can have hundreds of them. So you can end up doing a thousand pixels at a time rather than one. So if the CPU takes .001 second and the GPU stream processors are taking .001 second, the GPU will always finish the calculation first.