Wood density has a lot to do with the dulling rate of plane blades. Here is a chart of wood densities:
K&K used a wood of density 0.43. Inspection of the chart shows this to be in the range of redwood, pine, spruce. Beech, that David used, is rated in a range of 0.7-0.9, almost twice the density of the K&K species.
Do you think that the woods typically planed—needle wood, say, vs. temperate zone hardwoods—would have a bearing on included angle?
Similarly, the species of steel—say, Ward iron vs. PM V11–might matter.
Why would there be one single included angle that would be optimum over the full range of wood/steel combinations. Typical for Japanese kanna irons would be 25.