[benman94]

When playing back a DVD or other digital video file (say with a storage resolution of 720 pixels by 480 pixels) back on a device that outputs a standard analog NTSC-M signal, are we not loosing some of the horizontal resolution?

If my arithmetic is correct, the highest possible horizontal resolution for analog NTSC video would be ~333 lines, and that is for luma. On one of our vintage color sets with a color trap, or a cheap B/W set with 2 or 3 IF stages, it should be ~250 to ~280 lines, given that we're no longer working with the full 4.2 MHz of luma bandwidth. The ~330 line limit should hold true for any set fed via an RF modulator, and also for composite video. A set with component would obviously not be limited in such a way.

Why store the video on a DVD with 720 horizontal pixels then? Why not 640? 560? Cutting the horizontal storage resolution would save, if not tremendously, on storage space. Given the storage limitations of a DVD, and the fact that it came out in the late 1990s, one has to wonder why they specified 720 horizontal pixels in the first place? I don't recall finding a tremendous number of sets from the 1990s with component video inputs.