Which Warren Buffet engineered that way with his tax attorneys and accountants in order to avoid paying taxes, by taking his income in investments taxed as capital gains rather than as wages. Warren Buffet can say whatever he wants, but watch what he does: pay as few taxes as legally possible.
You essentially point out that progressive taxation means the rich should pay more, but can you justify that notion? Why should the rich pay a greater percentage of their income in taxes? If we're to be equal of individual value and equal of individual opportunity, how do you justify unequal taxation? Isn't codified confiscatory progressive taxation definitively biased?