What if the guy who earns $100K a year earns it by means of a monopoly on gasoline and charges the $15K guy $20 for a gallon?
Perhaps this will clue you in to the difference between a natural concentration of wealth and an unnatural one. What we have today is an unnatural concentration of wealth.
And the REAL income gap is much, much more than $85K.
You only get an unnatural concentration of wealth when criminal activity, such as graft, corruption and/or theft, is involved. The expanding income inequality in America is simply the concept of compound interest (read return on investment), and can be easily explained with simple math and common sense.
a. The magic number for doubling wealth (or income from wealth) is 72. Divide the rate of return into 72, and the dividend is the number of years needed to double that investment. This applies equally for $1 or $1,000,000.
b. If you start with $1,000 and a 6% annual rate of return, you can double that investment in 12 years. You now have $2,000.
c. If you start with $10,000 and 6% annual rate of return, you also double that investment in 12 years. You now have $20,000.
d. If you start with $10,000,000, and the same rate of return, you double to $20,000,000 in those same 12 years.
Consequently, when you start at a higher point, the amount earned is far greater, and explains why the rich almost always get richer, regardless of the economic condition of the economy. No conspiracy, no unnatural advantage, just simple math.