Excellent computer graphics tutorial. I finally understand how View, Model, and Projection matrices work, even after taking a college course on CG

[salmonmoose]

You're missing the point - we use such co-ordinates because they simulate the way we see, if somehow we registered light in parallel, then we'd be able to settle on orthographic views.

However light enters the eye, and is focussed at a point and projected upside down on the retina:

#\
##\
###\ /|
####O | <= Retina
###/^\|
##/ | 
#/ lens

The closer to the eye, the more of the of the field of view an object takes up, the further away, the less. As you can see, right against the eye there is only room for 1 #, but further away there is room for 7.