ANIMORPHIC: Many early DVDs did not bother with a 'true' (anamorphic) screen. They assumed the movie would be played on a 4:3 screen and mastered the movie INCLUDING black bars top and bottom in a 4:3 format. So now, when you play those movies, you get the original widescreen movie WITH black bars top and bottom (as part of the original mastering! of that DVD) then your widescreen TV plays the movie as it sees it, as a 4:3 movie (even though it is a widescreen with 'built in' black bars top and bottom, which also use up a portion of the bits.) so the sides of the 16:9 screen also have bars like for any other 4:3 movie.
Nearly ALL movies now are mastered as "anamorphic" or the image is the entire dataset, no 'wasted' bits on black bars at all, And the player sends the image it gets, so full 16:9 and whatever black bars you get with a 2.35 movie are just 'blank' and not wasted image.
(Look up anamorphic in wikipedia)
As for the menus... I think they use a different 'system' to create them, and they usualy just 'fill up' the screen no matter what. (I think?)
PS: a few studios STILL do not tell you it is anamorphic (or "enhanced for 16:9 screens) same thing, even though the movie IS.