The whole "richest fraction" argument is provably invalid (read,well, any of sowell's books on economics).
First, it's income, not wealth that is plotted (which skews the top due to single year sales of property or equities)
Second, it's not tracking people, but rather groups of people who's members change. If I remember correctly, in a decade, something like 40-50% of the bottom quartile move to the middle or top, and in a decade, more than half in the top quartile move down...we actually have a substantial amount of income class mobility in this country.
Third, it doesn't get broken down by age, the bulk of the lower brackets is composed of younger people, because, DUH, income increases with age/experience, which also accounts for a substantial amount of the bracket mobility.
Fourth, of COURSE ANY growth difference between brackets is going to result in an even more disparate amount relative to the total. What you are seeing is an effect of investment growth due to this country growing more focused on services vs manufacturing, the result of which is a more investment driven (and thus, more growth for those who invest.
Fifth, the big jumps are DUE to lower taxes, as lower taxes encourage capital movement (and thus, claimed "income" due to capital gains, rather than just letting equities sit there. (see my fourth point, which is also the reason increased capital gains don't generate substantial tax revenue is those with significant assets can CHOOSE when the transaction occurs, which is why increasing them hurts the middle class the most (for whom the most capital gain transaction is a home sale, which is not nearly as flexible in terms of life timing), and also why increasing INCOME taxes on "the rich" (which I guess is now $250k/yr for a couple also doesn't change this much, since the bulk of the "income" of the wealthy isn't w-2 wages, but capital gains (something this chart, as stated before) misrepresents.
And finally, why in all that is holy is the knee jerk reaction to economic growth by those with money (which is due primarily to investment and profit generated through business, is to tax (read:punish) them? It's the same false logic of people decrying oil company profits, while enjoying high returns on blue chip index funds in their 401(k)'s, and then whining when punitive legislation they asked for hits their investments--get a clue random people, there isn't some dude named Joe exxon-mobile out there raking it in, the bulk of most companies equity and debt is held by institutional investors...which make money on investments for, yup, anyone with a 401(k). Since the bulk of the wealthy are in the financial sector, they make money when their clients (which, for the absolute majority of invested dollars, are retirement funds) make money, so punishing the whole for doing their job is absurd.
This kind of misappropriated "logic" is not only grounded in mistruths, but is basically laughed at by those who actually bother to learn about the economy. And ironically, a far greater fraction of the uppernincome levels do understand the economy more than the lower levels, and use that knowledge to further their own success. It is this part that strikes me as most sad...those that complain loudest about wealth disparity do virtually nothing to transition forward or even educate themselves as to the real facts.
As was stated earlier...find bill gates on that income graph in 1980...or Michael Dell, or Steve jobs, or any one of hundreds of uber-rich. Better yet, pick ANY person, point them out when they are 21, and then point them out when they are 30,40,50,60yrs old...the VAST majority of those points will move upwards, regardless of who you pick (the age argument).
In summary, this is a class-warfare baiting bulls$&t chart that has no real use or utility other than demonstrating how little the user knows about taxes, revenue, the economy, or how markets work.
And, flame off...I'm just sick of how stupid "facts" get promulgated and thus de-educate those that might have had a chance.
