It's the same reason standard TV movies are fullscreen 4:3 while you can get either fullscreen and widescreen DVD's with the bars on the top and bottom. They crop off parts on either side of the film and "zoom in" on what's left to fill your screen. Since the focus of a movie is usually in the center of the screen it's not that noticable (although some, including myself, think it's a travesty to do that to a movie). Some times, when action happens on the edges of the widescreen movie, you'll actually see the widescreen image "pan" across, this happens a lot when people are talking on opposite sides of the screen in a movie. It's not as bad with fullscreen 16:9 as it is with 4:3, since you're not throwing away as much of the picture.