I have a 101, so my screen is smaller, and it is stand mounted in a corner. I only have one light, and it is plenty. Read up and ask questions in the bias lighting thread for specifics, but the general rule of thumb is that the closer it is to the wall, the more you need multiple lights.
There are any number of things which can and do happen which might lead to different perception of black, most of which I probably don't understand. But, for bias lighting, it is simple. If there is ambient light, your pupil allows less light in. Therefore, where the screen emits an extremely low amount of light, you will perceive pure black, rather than a situation where your pupil is dialated, and the screen is contrasted against a whole room of darkness.
Some sources may be of lower quality, resulting in less than ideal blacks. If the display is not calibrated properly, the black levels may not be right. And I believe it is pretty widely accepted that Kuros will have a darker area in the middle of the screen for the first X number of hours (no idea what that number is).