This way a designer can make a color as bright or a dark as he or she wants, and it will be displayed the same way on every monitor, if that monitor has been gamma corrected. Most video cards have a slide that can adjust the light levels in a game or application. However, Apple has gamma correction built into the Mac OS, so you may not need this feature. Also, many games themselves have brightness controls built in, so gamma correction is really an issue for older graphics cards and monitors. There are a number of ways to smooth these jaggies out, and these techniques are called anti-aliasing.
Jaggies are a result of using pixels.
Unfortunately, as long as we use little colored squares to draw images, we will have pixelation. Most commonly, an image is anti-aliased by taking two or four samples of the image and using those samples to create an image with blended colors at the pixelated edges to make the image appear smooth. It was previously impossible to implement these techniques in computer games, as the multiple samples would cut the speed of the game to an unplayable level. However, in the past year graphics cards became powerful enough to implement this feature, if at a cost of reduced speed or screen size. Nevertheless, many players have AA, as it makes for some very beautiful scenes.