Just a couple of points:
Remember, Buffett only reported a "taxable income" of about $40 million. Since that's less than one-tenth of one percent of his net worth, the tax rate he pays on that income does not affect him in any material way.
The fact that he does not (at least overtly) pay tax on the unrealized capital gains on assets held by Berkshire Hathaway clearly allows it to act as an effective compounding machine.
But the larger issue, in my opinion, is the extent to which the corporate income tax affects the return on capital to all shareholders, including Buffett.
It is often stated that corporations act more as "tax collectors" than as taxpayers. Analysts and economists speak of "tax incidence." In other words, upon whom does the tax burden really fall?
The following links offer a couple of points to consider:
http://gregmankiw.blogspot.com/2006/...tax-rates.html
http://www.taxfoundation.org/research/show/119.html
There's long been debate over how much of the tax burden falls on shareholders, but it certainly isn't likely to be zero.
Therefore, it can reasonably be argued that Buffett, as well as all shareholders, pays
some level of "invisible" tax on unrealized gains, even though it may not be very much -- at least expressed in percentage terms and in comparison to other tax burdens.
The shareholders "tax" would be the extent to which the corporate income tax affects the return on capital and isn't borne instead by consumers and employees.