Something I always wondered is: why do some games ask you to set the visible area of the display on HD consoles? Why do they have to do this? My HDTV is native 1080p, shouldn't automatically know the visible area to draw the game to and fit the game's viewport accordingly?
This is due to a phenomenon called overscan, which is a holdover from the CRT days of displays. It used to be that TVs and the signals sent to them were analog. Thus, there's was bit of a fudge factor in how the signal is sent to the display, and how the display renders it. In the CRT era, we'd send an overly large signal to the display with the expectation that some of it would end up being cut off by the TV.
In the digital era, most displays support 1:1 pixel mapping which means that the digial signal sent from the source gives precise information about where on the display to show each individual pixel in the image.
However, instances arise where the display maybe doesn't support it (or the game can't tell), or individual variance in displays would occasionally cause cropping around the edge of the display.
In situations where this is important (ie, a HUD that takes up most of the screen or which displays essential information near the edges), the game has to confirm where the edges of the screen are. This is usually done during an initial setup step, along with adjusting the gamma.