I don't think any of them really mean it. Not one. I think what they mean is they want to increase my taxes, not theirs. To be fair about it, maybe (just maybe) they would be willing to pay more tax if I were required to pay more, as well. But they are definitely not asking to raise only their own tax burden.
If all they wanted to do was pay more to the state, federal or local government themselves, there is absolutely nothing stopping them from doing precisely that. The federal government even have a handy "how to" faq providing an address to which you can send your filthy lucre:
So if, for example, Mr. Buffett really wanted to make more of his own money available to the federal government, he could send a check expressing his patriotism. And so can Messrs. Bronfman and Hastings and all those nice union members.
Citizens who wish to make a general donation to the U.S. government may send contributions to a specific account called "Gifts to the United States." This account was established in 1843 to accept gifts, such as bequests, from individuals wishing to express their patriotism to the United States.
Update: New Jersey does not seem to have that information available. Christie should have it added to the state's website.
But that's not what they want. At best, what they want is for me (and you) to be obligated to pay more, so that they can leverage their supposedly voluntary contribution. This is just another version of "Let's you and me spend that other guy's money" or, more bluntly, "I want your taxes raised."
Sorry, Mr. Buffet. I'm taxed enough already.