Zeev, in discussing whether a tax system is progressive or regressive, I'm not sure whether two examples (your wife versus Bill Gates) is sufficient to prove it to be progressive or regressive. Further, I'm not sure your wife's situation (self-employed, paying both the employer and employee's payroll taxes) is very representative. Certainly Gate's situation is not very representative. And as a another poster pointed out, Gates would likely be subject to the AMT, which could have the effect of significantly raising his marginal rate above the capital gains and super capital gains rates.
Having said that, I think the changes you propose to the tax system in the second half of your post make a lot of sense (although the changes you propose would seem to have little impact on the progressivity or regressivity of the tax system).