Shorthand for the old-fashioned Tin Pan Alley pre-rock and roll lovesong. It comes, I think, from the rhymes in "By the Light of the Silvery Moon", but I'll bet there were many other offenders. Robert Wyatt, on Soft Machine's "Moon in June", lampooned, with playful sobriety, this sort of sentimentality, a thread picked up later in Gang of Four's "Anthrax". These hipper-than-f*ck modern days have merely swapped new rhymes, clichés, and morals for old. Same crap, new wrapper.