720x480 can be 16:9 also, as can 352x480, 544x480, 528x480.
I think it has to do with the size and shape of the pixels.
720x480 is not the aspect ratio of the video.
Here's some confusion for you:
My DVD recorder records HD TV shows (from QAM cable) with a "dimension" of 720x480 with a "display size" of 544x480 and an "aspect" of 4:3. The image is distorted (squeezed on the sides). I change the aspect to 16:9 when I save and I end up with a 720x480 dimension, 720x480 display size with an aspect of 16:9 and the picture is correctly shaped as a 16:9 HD TV show.
When I author a video in VRD-TS, do I want 4:3 or 16:9 for display on a 40" wide screen TV (Samsung LN40B540)?
It depends on the source material and the source of the material.
A 4:3 TV program should display on your TV with Pillar Bars on the sides.
A 16:9 TV program will fill the screen.
A 1.85:1 Movie will have very small bars top and bottom. (letterbox)
A 2.35:1 Movie will have large bars top and bottom. (also letterbox)
You would then set the DVD player to the correct TV type and then use the zoom feature of the TV to spread/distort the image to your satisfaction/disgust. You always want to preserve the original aspest (OAR) in my opinion. You can almost always adjust the playback image but you can't easily recover the OAR after you distort/destroy it.
It's not. 720 x 480 is technically 3:2. But, the pixels don't have to be square. They can be squeezed in to produce a 4:3 (640 x 480) picture or stretched out to produce a 16:9 (854ish x 480) picture. When you save with VRD, selecting the aspect ratio will cause most players [other than Media Player Classic] to squeeze or stretch the pixels to produce that aspect ratio. This is very useful with some of my old DVD+R/RW recordings which are 720p or 1080i (16:9) down converted to 480i and squeezed into a 3:2 (720 x 480) frame. I just open them in VRD, click save and change the aspect ratio to 16:9. No major reencode required.