This example shows how our eyes see black as a contrast to white.
I lifted this photo from one of Tiddlers examples above and cropped out the area I found interesting. Tiddler mentioned in his post that he was getting good black levels with this panel he was testing and I saw it as a good example of what I have been talking about as perceived blacks.
The photo has several areas I tested with my color sampling tool the one I use is called (Visual Color Picker 2.6) and it's a freeware download if some want to try it out or mspaint has something similar I think.
In the screen shot I tested the black below the test panel then the brown area where no light is on the panel (basic screen lit with ambient light) then the white in the snow and finally the black of the truck and tire.
Results of color sampling in RGB values.
Border black 3 3 3
Basic screen 67 40 33
White snow 242 251 255
Truck black 76 44 33
Tire black 99 82 62
As the numbers point out the black of the truck and the basic screen with no light shining on it other than ambient are almost the same color. This idea is key IMO to the whole concept of understanding a neutral gray screen. It's not important to know in enjoying one though. I get remarks all the time as to how unbelievable black and shiny images look on my screen. If your eyes see it and your brain receives the information who am I to say its not really black.