They're probably referring to the backlight's brightness, as opposed to the overall screen brightness.
Backlights are actually very, very bright. It's just that only a small amount of light makes it through the LCD portion of the screen.
For example, surrounding the actual liquid crystal part are two polarizers, one at each end. The first polarizer knocks off 50% of the light right at the beginning, while the second polarizer absorbs anywhere from 0% to 100%, depending on whether the screen is white or black.
Also, an LCD screen is made up of 1/3 red, 1/3 green, 1/3 blue. If this pixel is red, that means that the green and blue light is filtered out. In other words, at any point in the display, only 1/3 of the light is getting through the color filter part of the LCD screen.
Another factor to consider is the aperture ratio. Each pixel is surrounded by wires controlling that pixel, which are opaque. This means that only say 75% of the light gets through the array part (the part that's controlling the pixels).
Putting all these together, this is 1/2 * 1/3 * 3/4 = 1/8 of the brightness of the backlight is getting through. This is assuming 100% efficiency, and assuming the screen you're looking at is all white. Actually efficiency is far from this, and people don't buy notebooks to stare at white screens, so altogether a very very bright backlight is needed to jam enough photons through that LCD layer to make only a miniscule amount of light that you see.