The main reason that they tax both dividend and inheritance tax is that they can. I know it's a flip answer but when they were creating this convoluted tax code many people were not affected by either taxes. However the Federal Government has been relying on the revenue for along time and it cannot easily be replaced.
Re: Inheritance tax - unfortunately you may have already paid taxes on that income but many people have not. Appreciation of assets doesn't generate taxes unless they are sold. The DEMS would like a $4-5 Million death tax relief going up with cola. The repubs want to eliminate it altogether. Eliminating it all is just plain insanity as this will eliminate close to a trillion over ten years. No easy answers once the government gets its hands on a revenue stream.
William Hung is to American Idol as Sarah Palin is to the Vice Presidency