This paragraph from Jonathan Franzen on the birth of the New Yorker story is spot on.

It was also in the fifties that “the New Yorker story” emerged, quite suddenly, as a distinct literary genus. What made a story New Yorker was its carefully wrought, many-comma’d prose; its long passages of physical description, the precision and the sobriety of which created a kind of negative emotional space, a suggestion of feeling without the naming of it; its well-educated white characters, who could be found experiencing the melancholies of affluence, the doldrums of suburban marriage, or the thrill or the desolation of adultery; and, above all, its signature style of ending, which was either elegantly oblique or frustratingly coy, depending on your taste. Outside the offices of The New Yorker, its fiction editors were rumored to routinely delete the final paragraph of any story accepted for publication.