In the case of fixed pixel displays of LCD panels & plasma displays, like CRTs the width/height can be adjusted and they can also have overscan areas where the edges of NTSC/PAL footage isn't displayed so for normal DVD content it's still up to the the screen itself to do the scaling of the input source because as far as I know they haven't made any flatscreens (LCD/plasma) that are perfect full NTSC or PAL resolutions so no scaling is done by the panel.
Which is why I'm not too fussed about that aspect of this tool.
As for outputting video at the right aspect ratio for projectors powered by PCs, they're 1:1 which is why there's a PC (1:1) output box on the page and I'll be producing a set of XviD files from the trilogy for myself that are 1024 pixel width at 1:1 aspect for my projector so it doesn't need to do any scaling.
I've changed the calculations so that they use the ITU-R BT.601-4 standards because that applies to the source material I'm working with, laserdiscs and for the moment I'm not working with recent high quality source such as HD or DVDs produced from HD masters.
Under the original set of calculations the aspect ratio of my French SW LDs came out at 2.29:1 but with the ITU-R BT.601-4 standards they come out at 2.35:1.
A friend of mine knows how to code javascript very well so I will ask him about beefing up the code so there's more input/output flexibilty without cluttering up the screen with a million and one options.