My wine gifts have always been from UA intl in F or in business, even though I fly AA much more. The wine giveaways seem to be triggered by polite and interested conversation with the FAs about wine or other topics. The gift always comes at the end of the flight, wrapped in a cloth napkin, and generally done "discreetly." I usually tuck the bottle away in my cabin baggage so that I am not seen by other pax with a gimme that they may or may not have received. I assumed that everyone experienced these gift cycles, but maybe it is the same few of us time and again.