But Gates and Buffett both say that they SHOULD be paying more in taxes - but they don't. So what they're really saying is, all those other guys (the "well off") should pay more, and then they'd pay more, too.
This supports the original poster's contention that the billionaires would seek that tax break (for "fairness") even if they didn't need it.
The well off don't pay much tax, and they will probably pay none at the top end (they'll donate to charity, for example, which they work at, and the charity will fly them around to their meetings, pay for accommodation, etc). Generally it's the middle class who end up paying tax until it's not worth working any harder.
Are you asserting that the government (and the public) will get more utility (benefit) from the extra 1 dollar on its $2.7 billion budget (increase of .000 000 04 percent), than I would from the extra dollar in my net annual income (on the order of a thousandth of a percent)?
That's a pretty incredible contention.
But on a percentage basis (in a progressive taxation scheme, and especially in the higher tax brackets) the government gets more marginal utility from a 1% tax increase than you would from a 1% tax break.
In any bracket and at any percentage, the government will be adding $x to it's huge budget by taking $x from an individual or organization's much smaller budget.
(* Note that it really isn't valid to compare marginal utility between entities. It's an individual, relative measure, rather than an absolute quantity.)
I don't know why some people seem to expect that of billionaires. It's not rational behavior for them or anyone else, so why do you think they should be behaving that way.
I've seen this more than a couple times in HN comments and it always befuddled me.