Actually, there might just be a point to it, but it's iffy. From what I understand of color sampling (which isn't much), only the luminance part of the picture (Y) is sampled at the "full" 720x480 frame size. The two chrominance channels (Pr, Pb) are sampled at half resolution.
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I understand that this scheme is also used for HD-DVD. Depending on how the downscaling feature works, it's possible that the equivalent of 480i 4:4:4 video could be output, which should result in sharper, more vivid colors. But you may not be able to detect a difference.