You know less than you think.
For U.S. states, as opposed to the Feds, there is much less difference between income and sales taxes than meets the eye, in terms of distribution.
Income taxes tend to have flat rate structures, as you point out yourself, as well as many of the dodges available to recipients of income from capital in the Federal tax code. Sales taxes tend to exempt necessities.
The most important point, however, is one that CTJ does not incorporate in their analysis because of their choice of methodologies. The use of annual incidence exaggerates the progressivity of income taxes and the regressivity of sales taxes. Income varies more than the sales tax base from year to year, so the variance of tax liability is higher, hence an appearance of greater inequality. Income not spent on consumption, and thus subject to sales tax, in the year it is saved will be subject to tax later, along with accrued interest, when it is spent (as most of it will be). In present value terms, there is less difference in incidence than meets the eye.
Of course, income taxes "can be" progressive, but so can consumption taxes, as you said. The reality that must be faced, however, is that neither tend to be.
On the whole, too much is made of tax incidence, especially at the state level, where income taxation is woefully inadequate to finance the public sector, and not enough of expenditure benefits. This defensiveness (a reluctance to defend public spending) does more harm than is offset by the advocacy of redistributive taxation.
>Pennyslvania is actually one . . .
MBS