When he says "It automatically scales 4:3, letterbox, anamorphic, and non-anamorphic movies to their correct aspect ratio," what he means is that it will detect whether or not the image being shown is within the aspect ratio--fullscreen (which should actually be referred to as 4:3 or 1.33:1) and widescreen (16:9 or 1.78:1)--set by the player. When it comes to letterboxed and/or non-anamorphic films in widescreen (they might be 16:9 Enhanced but missing the anamorphic "flag" command switch), the player zooms or resizes the image and uses a scaling algorithm to sharpen and clean the image. My HTPC does the same thing with a freeware program called FFdshow, but uses the much more powerful processing power of a computer and video card to do it a lot better. The important thing to remember here is that anamorphic transfers are not interpolating by adding lines. That is what scaling and resizing are for. There is no extra information in an anamorphic transfer outside of what is inside a 16:9 frame, it's the monitor using the full information from that frame.
As an example, let's use TR47's Collection. If I put the TR47s in the RP91 (or your friend's JVC, or my HTPC, etc.) set to output 16:9, the player notices that the image is non-anamorphic, however, it is letterboxed within the 16:9 frame. The RP91 (JVC, HTPC...) zoom (or resize in the case of the HTPC) the image to fill that 16:9 frame and get rid of the black bars outside of that frame*, run a sharpening and probably a noise reduction algorithm to enhance the image, and voila! A non-anamorphic, letterboxed DVD is presented in 16:9. If the monitor is 4:3 and isn't set to 16:9, it'll look exactly like an unsqueezed anamorphic image. However, it isn't the same as an anamorphic transfer, since it's adding information that wasn't there before, whereas the anamorphic disc (say from the Definitive Collection) retains all of the information because it's already set to fill the 16:9 frame. The players are fibbing, if you will, although that fibbing can make it look better than an anamorphic image from some Walmart POS player. That's why the RP91 (and it's brother the multi-disc RP82) was and is one of the most wanted DVD set-top boxes out there. Panasonic, cruel bastards that they are, woefully underestimated demand and for some reason stopped making them.
So, that's what's happening. Remember, no information is added in an anamorphic transfer! That's a misconception that, in this case has caused considerable and needless debate. And that is the end of that. If there are still any problems, feel free to PM me.
*Keep in mind that SW is ~2.35:1, so there are still bars on a 16:9 set.