Why do some DVDs fill my entire 16:9 screen and some still appear letterboxed?

Shouldn't recent DVDs fill up the whole screen (or at least have an option to), now that 16:9 screens are widespread? Or are some movies just shot in something other than 16:9?

 

Forget it.

- from a home theater forum"

"Often larger epic films, such as Gladiator, Titanic, and Star Wars are filmed with the wider scope of 2.35:1 to create a sense of being larger-than-life. Smaller, more personal films tend to favor the less gigantic 1.85:1 ratio. (However, I must say that this is a gross over-simplification as there are many exceptions to this rule.)

Since films shot in 1.85:1 are not nearly as wide, the empty space at the top and bottom of their widescreen presentations on home video will not be nearly as big. Here is a listing of some of the most common aspect ratios:


1.33:1 A standard television set; roughly equivalent to 4:3.
1.37:1 Referred to as the academy aspect ratio. The standard for films shot before the mid-1950s.
1.66:1 A bit wider than a standard TV, but not by much.
1.78:1 The dimensions of a widescreen television set; roughly equivalent to 16:9.
1.85:1 Popular aspect ratio for many movies.
2.35: Another popular aspect ratio for movies.
"