According to Starbreeze, one of the main reasons they're making this as a partial remake was because MS was unable to make Riddick BC with the 360, which makes some sense. There's probably a ton of code written specifically for Xbox's GPU and since MS doesn't have access to that anymore.....pfft. Sayonara . You know MS would have that game BC or up on Xbox Originals if they could.
This works out better anyway. Not only do we get what's supposedly a substantial chunk of new content but the game will also (hopefully) look a whole lot better too. Riddick on the Xbox was so weird. It was absolutely amazing looking at times but then a cinema would start and the game's resolution would get so freaking low that it looked like old Sega CD video.