Well, not really. When examining inter-generational income mobility, we see an interesting fact — adjusted for inflation and family size, the children of the top 20% earn less than their parent’s did at that age. The children of the bottom 20%, earn double what their parents did. (Figure 3)
Now, it is true that the median income increases faster in higher income bands than in lower. But one must recognize that it is not the same people in those income bands, and not even the same families. Also, basic laws of income distribution require that the higher bands grow faster than the lower.
The best mathematical model we have for income distribution is the Log-Normal distribution. Essentially, if you took the natural log of everyone’s income, the results would approximate a bell curve — a Gaussian, or “normal” distribution. When the median income goes up, and the standard deviation is scaled accordingly, the median incomes in each band necessarily go up faster in the higher quintiles.
This is not an increase is “inequality,” but the natural effect of the rising tide.