This is the very tail end of Fortune's richest people list.
http://www.forbes.com/lists/2010/10/billionaires-2010_The-Wo...
Any one of those people is worth 1 billion dollars, along with all the Gates's and Buffett's of the world. If I were pretty well off and worth, say, $1,000,000, it would take a thousand of me to equal one of him. And if I were a student with just a thousand dollars, it would take one million of me to get to one of him.
Based on that, the top quintile is not rich because of doctors, executives, basketball players or lawyers - it's billionaire company founders, investors, and the like. To test that hypothesis, I tried to find results marked by percentile, instead of quintile:
http://www.lcurve.org/WealthDistribution-1998.htm
The top 0.5% have 25.6% of the wealth and the next 0.5% have 8.4%.
---
(Side note, if you're thinking about income taxes: I'll bet there are more than a few people up at the top who get paid a dollar a year in salary.)