Not always the case, generally you are talking about things like writing off losses from prior years. For example, if you earned money for 3 years in a row and paid tax on those earnings, then you loose money one year, they don't give you anything back, so you get to write off you loss against future profits.
Besides, it does not make much sense to tax corporations. Think about it, they are not real people. They generally use their profits to pay dividends and wages in the future, which are taxable. So, if you tax them now, you will collect less tax on the other items in the future.
And if they use it for wages, now you are also collecting SS and other payroll taxes, so when you tax a corporation, you often end up with less tax revenue, you just collect it earlier.
However, you are correct, the middle class always gets squeezed, especially the upper middle class.
And as you start to become rich, there are a lot of unfair things, like AMT and excess Medicare tax, and phase out of many tax credits and deductions, etc.
Sorry Jeff, just had to correct the record! Too many phases get repeated and repeated w/o ever thinking them through.