That's not actually correct...
What Mort described is the ability to see the individual pixels that make up your image.
Screen door is something that could be confused, but is not the same as seeing pixel structure.
If you think about each pixel on a screen, it is individually fired up... and between each and every pixel there is a small gap that separates it from the pixel next to it. In many commercial projectors and a lot of older projectors the gap between pixels was quite noticable. Since pixels in projection using LCD and DLP are square, the gaps between each pixel created an effect that looked like a screen was put on top of the projected image. Little black lines, gaps in the actual video, were clearly apparent, even at 10+ feet back from an 8 foot screen.
Nowadays, the black lines, or screen door has been minimized to the point where at about 5-7 feet you can start seeing pixels, but not the screen door effect. At about 3 feet you start to see the black lines between the pixels which is the screen door effect created by the LCD or DLP matrix.
I am not sure how much plasma or LCD flat panels suffer from screen door as the pixels are much larger than they are in a small projector where the pixels are converted from a chip that is 1 inch across to a screen that is 92 inches wide. That gap is magnified 92 times! More if it is only a .7 inch (or smaller) DLP/LCD.
Plasma & LCD flat panel displays (FPD) are not magnified so any distance between pixels should really be close to non-existent. You should really need to be just a few inches away from the screen to see any gaps in between each pixel. But, at that distance, each individual pixel is also visible so your image would suck anyway.
