The secret element in black and white pictures is the lack of colour. Don't roll your eyes just yet. Give me a second.
Photographs are meant to capture, for posterity, a particular moment. But looking over that moment afterwards, colour photos don't leave any room for nostalgia to play out its bit. In a b&w, we can imagine the near-white dress as being a cloudy cream chiffon, and the greyish face as being a beautiful golden-brown. Our imagination does the Photoshop-ing. And the imagination, no matter whose it is, is good at that sort of thing. Better, I dare say, than Adobe.
A colour photo is horribly real. Who on earth wants to remember that first date as the itchy, hot, awkward, altogether silly thing it was ? They looked nice, in the dress and the suit, they had their best smiles on, everything else we can imagine into place.