You're kidding right? GDDR5 RAM is basically extra GPU power - essentially making the PS4 have no ram.
The reasoning behind this is because the CPU and the GPU on the customized AMD chip is completely integrated within the entire system. It has a RAM module built into the chip for basic tasking whilst the GDDR5 RAM is meant for game oriented tasking on it's entirety. All multimedia runs through the GPU as well as the CPU module.