Many users don't have expensive monitors, so they can't calibrate the monitor successfully. This is a problem when many web designers only test their site on a mac in a nicely lot office.
Thanks for the link! I've seen the site before but never thought of testing my screen when I got my new laptop.
It's very difficult to tell, though. The gamma varies between 1.9 and 2.3 (roughly) depending on the angle at which I look at my screen. Every time I sit this will be different.
Opening the article again, it also depends where I look: when tilting my laptop back a bit, the text appears darker (even black if I tilt it far enough) but the exact shade differs: near the bottom of the page it's still greyish while the top part is indeed almost black.
Looking on my phone, it's a lot better readable than on my laptop, probably because I look at my laptop screen at an angle and my phone's colors don't change if you look from the far top or bottom.
The worst color change I recall seeing on a laptop was the background color Google used to use to identify ads (a pale yellow as I recall). On cheaper laptop screens even the slightest tilt would make it white, making the ads indistinguishable from real results.
If you have something like the Nvidia Linux control panel for adjusting colors, lowering the white level and raising the black level can help compensate a bit. The open source Media Player Classic (or MPC-HC maybe) player also has a nice shader to correct for the vertical variation, but I don't know of any way to apply it to the whole OS.
http://contrastrebellion.com/ !