Remembering a conversation I had moths ago with Chris Lemon about this topic, it goes back to why you would not want to equate "stopping the game" with "I quit!" or why a tie should break in favor of the person who didn't stop:
What if you're on 20? If the other guy has 21 you're cooked anyway and the game will be over. Worst case is a tie at that point. Sure, you could play another round, take your dopey 1 point question, reach 21 and the game would be complete, but that allows your opponent another chance to do the same. You lose zero by calling it good and comparing the scores at that point. You could extend that down to probably 17 or so, because a 4 point question should still be a lay-up, right? At 17 you run the risk of losing, and that risk isn't there at 20.