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> make moving pictures appear seamless
True enough.
NTSC is 30fps, while PAL is 25fps.
The overwhelming majority of people were happy enough to spend, what, billions on screens and displays capable of displaying motion picture in those formats.
That there is evidence that most(?) people are able to sense high frequency PWM signals doesn’t make the claim that 15 to 20 frames per second is sufficient to make moving pictures appear seamless.
I’ve walked in to rooms where the LED lighting looks fine to me, and the person I was with has stopped, said “nope” and turned around and walked out, because to them the PWM driver LED lighting makes the room look illuminated by night club strobe lighting.
That doesn’t invalidate my experience.
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Even a person with below average eye sight can easily see 24 fps judder in fast moving pans. Vision is not nearly as simple as people want it to be.
> NTSC is 30fps, while PAL is 25fps.
That's not really right. Most NTSC content is either 60 fields per second with independent fields (video camera sourced) or 24 frames per second with 3:2 pulldown (film sourced). It's pretty rare to have content that's actually 30 frames per second broken into even and odd fields. Early video game systems ran essentially 60p @ half the lines; they would put out all even or all odd fields, so there wasn't interlacing.
If you deinterlace 60i content with a lot of motion to 30p by just combining two adjacent fields, it typically looks awful, because each field is an independent sample. Works fine enough with low motion though.
PAL is similar, although 24 fps films were often shown at 25 fps to avoid jitter of showing most frames as two fields but two frames per second as three fields.
I think most people find 24 fps film motion acceptable (although classical film projection generally shows each frame two or three times, so it's 48/72 Hz with updates at 24 fps), but a lot of people can tell a difference between 'film look' and 'tv look' at 50/60 fields (or frames) per second.