Like probably about 90% of games RD2 is a console game ported to PC, consoles at this point are still GCN + Bulldozer, 6 cores for the game and 2 for the OS and background services.
RD2 is a really bad example of a PC port, there is a company, (i forget the name of them) who do the vast majority of console to PC ports, they do an outstanding job of it which is why the vast majority of game developers outsource that to them, except RockStar, who do that in house, and not well.
Consoles right now are very different to PC, to get the most out of relatively weak hardware there is no API layer between the game and hardware, much like Mantle used to be, Vulkan is based off Mantle but it now has an API layer to make it Hardware Agnostic, when you're porting a game designed to run on the metal of very specific hardware to run on multiple hardware configured machines, PC's, and you don't do a good job of it, its not a healthy experience.