this was first used during WWII for "died in action"; the story goes like this:
Young soldiers often asked one another what they planned to do when they returned home after the war. A common reply from those hailing from rural regions was that, upon returning, he would marry his girlfriend, buy a farm near his home, and raise children. Upon hearing of the death in action of such a fellow, a man would say with sad sarcasm, "He's bought his farm."
on a related note, I used to play pocket billiards with an old fellow who, when I set him up for a game-ending runout, would intone, "Now you've sold the farm."
