It turns out this phenomena is global in nature. From Metrics 2.0:
"The wealth of high-net-worth individuals (HNWIs), people with net financial assets of at least U.S. $1 million, excluding their primary residence and consumables, climbed to $33.3 trillion in 2005, an 8.5% increase over 2004, according to the 10th Anniversary Edition of the World Wealth Report, released by Merrill Lynch and Capgemini.
The Report found that the number of HNWIs grew by 6.5% over 2004, to 8.7 million, and that the number of Ultra-HNWIs — those who have financial assets of more than $30 million — grew by 10.2 percent, to 85,400 in 2005."
Interesting stuff . . .
Global High-Net-Worth Population Grows to 8.7 Million, Worth $33.3 Trillion