I am now plugging in my MacBook to my Panasonic PT-AX200U projector. In the Displays Preferences in OS X I have an "Overscan" option. By default this option is checked.
So, I unchecked it, and I get a black-rim around the screen. If I activate the "Overscan" option, what I seem to get is pixel-to-pixel mapping of the 1280x720p rez.
So in actual fact most of the time you want the "Overscan" option checked for this reason, and only uncheck it to compensate for those TVs that overscan. ie. Unchecked "Overscan" actually shrinks the image and adds a blank black rim (which the mouse pointer can enter by the way) to act as an "anti-overscan" for specific TVs, thereby blurrifying the picture. Is this correct?