Proof of the old chestnut?

1) Does " proof of the old chestnut" mean what?
2) Does "every hack with a keyboard" mean "every hit on a keyboard"?

Context:

............
The diplomatic memoir is an even bigger hurdle, for diplomats by definition are, well, diplomatic. (Hardly anyone actually really read Dean Acheson’s 1969 memoir but every hack with a keyboard, including this typist, has quoted, and misapplied, its title: “Present at the Creation.”)

...............
“Hard Choices’’ is destined to be a book that is purchased but not read, a volume given but not opened. Indeed, it is impossible to imagine very many of the more than 318 million Americans alive sitting down and reading the whole thing, unless, like me, they were paid to do so, and even I admit to skimming the chapter on Latin America — proof of the old chestnut, sometimes attributed to James Reston, that Americans will do anything for Latin America except read about it.