I've looked at the recommended specs as oposed to the minimum specs and it says 4Gb minimum and 8Gb recommended. Why? FC3 is a 32bit app and is impossible to address more than 4Gb anyway. My PC has 8Gb and task manager says only 3.2Gb is used running FC3 for an hour as well as all the other stuff like to OS etc. Is this just marketing trying to push hardware sales?
It is because with your operating system and any other programs running, in addition to Farcry 3, could require more than 4GB of RAM. It is recommending 8GB so that there is little to no chance you will run out of available RAM.