Shane,

I do not believe the average corporate tax rate for all U.S. corporations is that low today. I think that number you are showing is the average for large corporations a couple of years after a severe recession. Here's why it is not as meaningful as you apparently believe it is:

1. Many large corporations have significant profits from overseas operations. If those profits are not repatriated, then no U.S. taxes are owed on those profits. Further, the taxes owed when overseas profits are repatriated are reduced by the amount of taxes paid to foreign governments.

2. Any large corporations which had losses during the severe recession would be able to use tax-loss carryforwards in subsequent years. Those are temporary shields to corporate taxation which likely have little bearing on current taxes.

3. Average effective tax rates are meaningless to the individual firm. As many as 20% of Fortune 500 firms may pay zero taxes in some years. But many others will pay much higher rates than the average rate.

4. As I've pointed out in both the note you responded to, and in a subsequent note, it is the expected marginal tax rate which firms must use in deciding whether to invest further in the U.S.