The problem is the way TVs stretch pictures to make a 4:3 picture into a 16x9 one. Usually the "stretch" the edges more than they stretch the middle, the result being that the bulk of the viewing area where all of the action takes place isn't as distorted. So the Trek DVDs can be stretched by a TV (or player) without too negative an impact on the picture. The most you'll see is some distortion between "the middle" and "the edge" and some "lensing" with lines and objects on a scan.
The TNG Blu-Rays are matted. On your standard settings the sides of the picture are black (easier on the TV, can prevent uneven wearing on the pixels) as opposed whatever color your TV uses for areas without a picture. The result is when use your TV to stretch/zoom it stretches the entire thing, including the black "matted" area which causes a much more distorted picture than you'd have with DVDs.
Excuse the quality of these pictures, took them with my camera so the quality is iffy. But it's less the colors and such I'm going for her and more the proportions.
From the opening scene of "The Child"
The BD on "Full" Screen (Maintains OAR. Shows the black "matting" used by CBS to frame the 4:3 picture.)
orizontal-Fill" (Stretches picture horizontally, cuts off edges of picture.1)
On "Just"(ify) (Stretches picture to get the corners of the picture to fit the corners of the TV. Stretches the edges more than the center.)
Om "Zoom" (simply zooms in on the center of the picture. Ratio is likely whatever it takes to make a 4:3 picture fit on a 16:9 screen. Wildly cuts of parts of the image and can make things look blockier or out of focus.)
DVD on "Full" Screen. TV stretches it to fill the screen Stretching is more severe than either with Justify or H-Fill.
DVD on "H-Fill."
DVD on "Just."
DVD on "Zoom"
(My player also has a "4:3" setting which makes both pictures exactly the same. The 4:3 picture in the middle with light-gray edges. This can cause bit more wear on the TV and is less pleasant to look at (IMHO.)