As for FC3 DoF.. I get it. The game is so incredibly detailed up close, that keeping that lvl of detail in the distance would kill even the most ambitious PC gamer rig out there. Now they can do one of two things: 1. They either present the delusion of a lush jungle in plain view by giving you a distant surface so bald it's like the entire island got cancer or 2. They blur it out so they keep the illusion safely confined in the beautiful lush environment you're in by blurring out the distance.
That's you. That's why I posted that's not how Depth of Field works and that in Far Cry 3 Depth of Field has a negative impact on performance, disabling it actually improves performance. Don't take my word for it, go try both before posting about it next time. If you like depth of field then bully for you, no one is telling you not to but don't say they do it because its beneficial performance wise for people because that's not the case.