The 16:9 aspect ratio of HDTVs was a compromise. It supports widescreen view programming, but lets older 4:3 TV content not look too bad. It is equivalent to a ratio of 1.78:1
Hollywood has always loved widescreen presentation formats. Think Cinemascope. Most movies run anywhere from 1.85:1 to 2.5:1, resulting in letterboxing on your 16:9 HDTV. You'll just have to live with it.