Example shots from Beyond Good & Evil (NTSC-USA), a game with no progressive support. Keep in mind this game runs with permanent letterboxing by design.
Native 480i (really 448 lines)
Forced 480p (true 480 lines)
Noting BG&E's letterboxing, it's interesting to note that the additional 32 lines are in the visible area and the bars are the same size (in pixels) as before. There's some occasional glitching in the bottom 32 lines of visible area in BG&E, presumably because the game never intended to display those lines.
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Here's F-Zero GX (NTSC-USA), a game with native progressive.
Native 480p (really 448 lines)
Forced 480p (true 480 lines)
You can see quite well here that the game continues to render at the same field of view in both modes: the ship is slightly taller in the second shot. Though the latter renders with slightly more detail, it's likely the 448-line display more correctly renders the intended shape of the image. However, the difference is minor and only really noticeable if focusing on geometric shapes like circles or squares.
This isn't really a bug report, just pointing out a peculiarity of the way this has been implemented. I haven't tested extensively enough to say whether every game handles the extra lines the same, e.g. some might actually increase the visible area rather than simply "stretching" the picture.
