I'm not sure that I agree with the stiff versus soft characterization. As with other characteristics when taken in isolation, there are a number of exceptions to any rule (the long-running "discussion" of the Metron:B5's ability to carve at high speed is an example of this). Length also makes a significant difference (a stiffer ski skied shorter may perform very similarly in many conditions to a softer ski skied longer).
However, I think a section that describes the basic characteristics of a ski (longitudinal flex, tortional flex, sidecut and width, running length, turn-up, etc.) would be useful. I, too, have to reread it.