Re: A flat tax is a proportional tax.
There is indeed an upper limit imposed on all flavors of payroll taxes: you need to earn a salary to pay them (many of them, anyway). The higher up the food chain you get, the less likely you are to earn a paycheck. Furthermore, since the wealthy folks can spend so much to lobby, they can have the sorts of earnings they get from their place of business declared by law as not payroll. This is how Romney is able to claim his income from his Job at Bain as not normal income subject to income tax rates. And how he pays at a lower rate than his secretary.