Three reasons: You sit much closer to a computer screen compared to a TV, so your peripheral vision has a better chance with the computer screen to see flicker. Computer CRTs supported higher refresh rates, so they used phosphors with shorter afterglow (otherwise you'd get ghosting/S&H-like artifacts like TFTs produce). You can notice this one when you photograph a computer CRT vs. photographing a TV with the same shutter speed. And at the end of CRT TVs a lot of them were 100 Hz.

Interesting hypotheses, though I still can't quite accept them as final. I seem to recall that the effect was much more noticeable, not only when sitting in front of the screen—basically enter the room and there it is. And I think that I've experimented with lower refresh rates too, at least I definitely had the time and inclination—but can't remember if the monitor allowed them with the available resolutions. It's stuck in my memory that only 60 Hz does this.

When I get rich and have lots of free time, I'll probably buy a bunch of old CRTs just to dig to the roots of this.

Btw, I count only two reasons there.

(1) You sit much closer ... (2) Computer CRTs supported ... (3) And at the end ...

The LCDs you see this on are 6-bit color displays using temporal dithering to pretend to be 8-bit color.

The reason for flickering on specific patterns is independent of temporal dithering. This is caused by cyclic polarity inversion: http://www.lagom.nl/lcd-test/inversion.php

(temporal dithering usually is visible as slight noise on darker shades)

That's why drop shadows look horrible when I'm looking at my screen at the wrong angle... I knew it was a dithering thing, forgot LCDs were 6-bit.

Only cheap/low-end LCDs are 6 bit. Most are 8 bit with no dithering.

Should this be the case with a Macbook, even if a sorta old one? Because that's the machine I've seen the flicker on, for the past bunch of years.

AC power is 60hz so room lighting (especially florescent) also flickers at 60hz. It’s a sort of wagon wheel effect.

I dropped a hint right there that the AC frequency is definitely not 60 Hz where I am.

Actually you didn't. There were many countries that used PAL for TV broadcasts but have 60hz AC.

They didn't say PAL, they said "50 Hz TV."

PAL and 50 Hz TV are not synonymous. Brazil has 60 Hz AC and uses PAL-M which is 60 Hz TV. AC=TV even in these odd cases.

Old CRTs couldn't possibly clock their flyback to anything but mains.

Hmm, afaik the framerates were chosen to be equal to the AC freq so that there are no glitches in the image. Do those countries have converters or something in the TVs, or did they watch jumpy image?

Fluorescent lighting, assuming it's not starting to fail, flickers at 120 Hz because each half cycle lights it up equally (+ or - doesn't matter). Incandescent also has 120 Hz flicker but the valleys are almost as bright as the peaks (slow response) so it's essentially imperceptible.

Cheap LEDs like some holiday minilights are rectified so they'll flicker at 60 Hz and I can't stand them.