I agree that the quote is interesting, and agree with happydog that the idiomatic expression has an existence independent of the original quote. Somewhat similar examples that strike me include “head over heels” (it was “heels over head” in the original quote, or “hele ouer hed” if you want to be a real stickler, and it appears to be about the prophet Jonah tumbling about in the belly of the Leviathan, not a person being overwhelmed by love) and “beauty is only skin deep” (from Overbury’s poem, “A Wife”, the line was, “And all the carnall beauty of my wife is but skin-deep, but to two senses known;"). The “two senses” appear to be sight and imagination, as all flesh feels the same at night. Overbury was later poisoned, but, surprisingly, it was apparently not by his wife.
At the risk of making a broad generalization, it strikes me that original quotes are often considerably more striking turns of phrase than the idiomatic expressions that they spawn, but the original quote is often too focused in its references for it to be useful as an idiomatic expression of general applicability (or it is otherwise ill-suited to that purpose), so it is not surprising that the form of the quote often shifts as the phrase becomes a popular expression, and that its meaning either broadens or changes in the process.
