This is "real" income?
Adjusted for inflation, right?
EVERY quintile has risen; with the top quintile, obviously, tied directly to investment income (look at the boom Clinton years). So, the people who stand to gain the most from investments, do so.
What is not demonstrated is all of the money people have made and invested that DOES NOT show up on this graph. All of my employees (all in the 99%) have 401K accounts - and all are vested; well over a million dollars tied up in those accounts, none of which has EVER been reported as "income". It will be, eventually; but only after those people retire, and it becomes either primary, or secondary to their SS - but, nevertheless, never enough to cause a blip on the chart. There are trillions of dollars tied up in 401K's around this country; only those in ROTH accounts (a great minority) are represented in your chart. BTW, why is 1979 significant? It's the year 401K accounts were born. They've been reducing taxable income (the measured statistic on the chart) ever since. Will it make up all of the difference? Probably not, but it would certainly make for a better representation of what is going on; the 99% are benefiting from, and paying for, the performance in the market, but it is in, largely, unreported income.