> sibling commenter's observation of income, not wealth, is astute
In the U.S., at least, income and wealth are highly correlated, so there isn't a huge distinction to be made. There are indeed some wealthy people with low income, and high-income people with low wealth, but it isn't the norm. See table 5 (pg. 36) in this whitepaper, which shows both net worth by income percentile, and income by net worth percentile: http://www.federalreserve.gov/pubs/feds/2009/200913/200913pa...
Example numbers: the top 1% of 2007 income-earners held 26% of U.S. wealth, and the top 1% of households by net worth in 2006 earned 16% of the year's income. Meanwhile, the bottom 50% of income-earners held only 14% of U.S. wealth, and the bottom 50% by net worth earned only 22% of U.S. income. The general trend holds in the in-between categories as well: the 95-99th percentile of incomes hold about twice as much wealth as the 90-95th percentile, etc.
So the relationship is not perfect, but taking the groups in aggregate, higher-income-earners control considerably more wealth than lower-income-earners. Some of the later figures in the document explicitly plot some ratios.
Progressive taxation also has relatively little impact here. If you converted the income tax to an implied wealth tax (i.e. take tax paid in a year divided by wealth held at that time), U.S. income taxes are in aggregate roughly equivalent to a flat tax on wealth.