This is surprising how, exactly?
The PS4 is constantly recording the last 15 minutes of high-def gameplay. Where did everyone think all that live data was magically going to be stored? Streamed to the hard disk?? No way a typical 2.5 SATA notebook drive could handle those data writes while simultaneously reading game data. RAM is the logical place to store that 15 min backlog of gameplay.
Even at that, I'm sure Sony is being very conservative in what they are allocating to the OS/video capture cache vs. game RAM. I'm sure as they reduce the footprint and increase efficiency of the OS/video cache they will 'give back' memory to game developers to use. It happened at least a couple times durting PS3 lifetime. Much much harder to try to reclaim RAM for the OS later on than to give it back.
