Here's the chart I'm pretty sure you're thinking of: http://s.wsj.net/public/resources/images/ED-AH556B_ranso_200...
from the 2008 Wall Street Journal article titled "You Can't Soak the Rich": http://online.wsj.com/article/SB121124460502305693.html
The phenomenon is called Hauser's Law: http://en.wikipedia.org/wiki/Hauser's_Law
and intelligent criticism of the chart can be found here: http://www.portfolio.com/views/blogs/odd-numbers/2008/05/20/...