Interesting point. I wonder if it is because the upper bodies and arms and heads are cut out, that you get far more of a 3D appearance to the block of troops.
I think its absolutely this. I've seen other paper soldiers which while nice still have a large expanse of white paper around the figure and it completely destroys the illusion (though someone once did ECW armies in black and white purposively to mimic period engravings and it looked quite nice).
I'm looking forward to all the future books, seems we are getting Romans-vs-Gauls, 1066, Wars of the Roses (this year I think), Spanish Succession and American revolution. From my own experimenting fixed bayonets are a bit of a challenge, so it will be interesting to see how those are tackled.