You should do some research on 240p. There is no such thing are "240i".To the first part, that's interesting to hear. You have a link to some information that explains why higher resolutions exhibit dot crawl more? Even still, what I said stands, regardless of its severity (though it becomes moot in the context of what I replied to).
To the second, I'm a little confused here.
These old consoles output a 240p (progressive) image. From what I understand, unless you have an expensive RGB adapter for, say, PC CRT, you have no choice BUT to use an old school sdtv that will interlace the original image.
So how is that a requirement for true 240p? Sounds more like a lack of choice than anything.
Edit: Unless you're saying, in order to get true 240p output, you'd need a display that can output standard definition resolutions - non interlaced.
If that's the case, again, this composite only GXtv won't give you true 240p. Its 240i
If that NOT the case, and you mean a display that can output at 240 - independent of interlacing....then how is it TRUE 240(p)?
When using 240p mode only the even scanlines are drawn while the odd scanlines are left black. This creates a lower resolution but more stable image. 15 khz 240p is different than what you'd see on a PC monitor outputting at 320x240.