I explained why clearly in the context of the post (at least, I thought so!).
I will expand upon the topic, although this REALLY belongs in the DVD hardware forum.
1) What format is DVD video?
DVD video is inherently 4:3. Say it, slowly -- this is the number one most misunderstood characteristic of DVD video. DVD video is inherently 4:3.
Video is stored in three ways:
A) 4:3 full screen. In this format, motion pictures are cropped to fit the 4:3 window, then saved to the disc.
B) Letterboxed or matted. In this format, motion pictures are saved in the 4:3 frame so that they fit in the 4:3 window with their original aspect ratio (OAR) intact. There are black bars at the top and bottom of the 4:3 window; resolution is lost because the picture is smaller than the available scan lines.
C) Anamorphic or enhanced. In this format, the motion pictures are saved at the proper verticle height to fill the 4:3 window; instead of cropping the edges like you would for 4:3 fullscreen, the image is squeezed sideways, squished to fit the 4:3 window.
2) How does an interlaced player present these formats?
An interlaced player sends the video in the 4:3 frame to the TV. The TV can be set for three modes.
A) 4:3 Fullscreen. This is propper for cropped movies, or for video that was full screen to begin with (like many TV show season collections). In this mode, with the F38310, there are grey sidebars added to fill the 16:9 screen.
B) "Full". This is a zoom mode for letterboxed movies. In this mode the TV expands the 4:3 frame presented by the DVD player in both the horizontal and vertical dimensions to fill the 16:9 screen.
C)"Fill". This is a stretch mode for anamorphic movies. In this mode the TV stretches the 4:3 frame sideways to fill the 16:9 screen.
Please note 1, for the letterboxed and anamorphic modes, if the video is in an OAR of 2.35:1, there will be small black bars at the top and bottom of the video. An OAR of 1.85:1 or 1.77:1 will effectively fill the 16:9 window.
Please note 2, it is the television, not the player, which is doing the scaling in interlaced mode.
3) OK, well, how does progressive video change things?
Well, not all televisions which can accept a 480p input can scale the video internally. It is a case of too much video information, I guess. Specifically, the F38310 can't scale 480p or 1080i. The set treats all 480p and HDTV as inherently 16:9. Most progressive players perform internal stretching of anamorphic/enhanced DVD. This video will properly fill the 16:9 window of the F38310 and other HDTV's like it which don't scale progressive/high definition video. However, most progressive DVD players will send 4:3 fullscreen video and letterboxed video as 4:3 -- and because the F38310 locks in 16:9, you then can't scale the video to fill the screen. Some players, specifically those with a genesis video processor, CAN perform scaling before the image is presented to the TV player. 4:3 fullscreen and letterboxed material can be forced to several zoom modes with this type of DVD player.
For example, the Panasonic RP91 is highly thought of (go over to the DVD Hardware forum and do a search). It has 4 modes for 4:3 video: Normal, the image is stretched horizontally to fill the screen; Auto, properly flagged letterboxed DVD's are zoomed; 4:3 fullscreen video is presented in "fullscreen" 4:3 mode (non-zoomed); Shrink, all 4:3 video is presented in 4:3 fullscreen (non-zoomed) mode; Zoom, all video is presented horizontally and vertically zoomed for letterboxed material to fill the 16:9 screen. There are a few players (not the RP91) with "free zoom" modes which can zoom a 2.35:1 movie to fit in the 16:9 screen without any black bars at the top and bottom, however, you lose a little bit on the right and left edges.
There is a tradeoff for the ability to zoom 4:3 progressive video: generally, people consider other video chips, such as the Faruodja/Sage video chip, to handle deinterlacing better than the Genesis chip.
4) So what are my choices if I have a TV like the F38310?
Well, you can buy a cheaper player like the Panasonic RP56, with the sage/faroudja chip, which everybody speaks very highly of, and, when there is letterboxed material you want to zoom, switch off the progressive output, and view the material in interlaced mode. The F38310 will be able to zoom the image for you, and will internally upconvert the 480i to 540p.
Or, you can go with a player that zooms progressive video for you. generally this will be a player with a genesis video chip, and there are several good ones out there. Cheap ones won't handle deinterlacing as well as those with the sage/faroudja chipset, however a few of the more expensive players like the Panasonic RP91 do a very good job.
As to HBO-HD, Showtime-HD, and digital OTA television, if they are broadcasting in 480p or above, you can't zoom it. High-definition prgramming is 16:9, so it fills the TV window. unfortunately, most programming on OTA netork digital feeds,and quite a bit on Showtime and HBO-HD, isn't really high definition. This other programming is "upconverted" NTSC 480i 4:3 video. Being originally 4:3, when your TV gets it in 480p, 720p, or 1080i, it can't zoom it. This is a pain for shows like "ER" on NBC -- my wife can't zoom the digital feed, so she watches the analog, using the TV set's zoom mode to fill the TV window. Digital OTA stations do have a choice -- they can send the 4:3 in the OAR or they can play with the aspect ratio. The best results are when they zoom the video as you would the letterbox format, and then squeeze the video a little bit vertifcally -- cropping it at the very top and bottom of the screen. This fills the screen without distorting the video quite as much as stretching it sideways to fill does.
Hope this helps,