Well, if you read closely, the 70 rate is cutting to the sum above the threshold value. So if your salary is X + Y + Z, where X, Y, and Z are, respectably, the lower, middle and the high threshold values, the taxes you pay is something like

(X * alpha) + (Y * beta) + (Z * gamma)

and only `gamma` is 0.7, `alpha` is something like 0.35 and I assume `beta` is something in between.

So those who pay 70 percent taxes are already maxed out on the lower contributions in corresponding income range.