Originally Posted by chni
Because producing an other resolution (i.e. producing black stripes left and right) has nothing to do with the type of connection to the monitor device.
There are two approaches to solving this problem:
1. the card outputs a 16:9 aspect ratio. E.g. a resolution of 1280x720. the monitor will display it fullscreen and the game, being 4:3, uses only the center part of this area leaving black bars on the side. Problem of the game when it cannot do this.
2. the card outputs a 4:3 aspect ratio. E.g. a resolution of 1024x768 or 800x600. The game uses the full screen area and your monitor is responsible for fitting this on the screen. Problem of the monitor when it cannot do this.
With DVI there are scaling options in the signal that can direct the monitor to do the correct scaling. With VGA there aren't, except for the sync polarity. So the connection of the monitor device really affects this, even when you don't believe it.
The scaling should be configurable in the monitor when you want complete control, like in a TV set.