It turns out that investor amounts are not Pareto distributed (the continuous analog of Zipf's law), but rather a mixture of two log normally distributed random variables.
That's interesting.
The first thing I thought of when I saw that was that when JD first launched, I gave some 250 or so separate gifts of 0.01 BTC to forum users. Many of them were probably invested and forgotten. Could those account for the "small investor" group, or isn't it in the right place for that?