Kevin, Excellent article. This is obviously geared toward beginners, and the concepts you illustrated provide a very good stepping stone to more advanced education.
One MAJOR concept that should be included when discussing avalanche terrain is slope convexity vs. concavity. Convex slopes, even if the they start at shallow angles, are exceptionally weak, and can act as dangerous trigger point for much larger avalanches. More info here: http://www.fsavalanche.org/encyclopedia/convex_slope.htm