I've noticed that as well. Whenever I'm throwing with a friend, I try to throw a breaking pitch but it just doesn't seem to break like it would in comparison to one in a game. I'd guess that the eyes try to fool the pitcher after he's thrown his pitch. For instance, if I throw to one of my friends and it hardly breaks then I ask them. If they say no then there's no controversy there. However, when you're throwing in a game and the ball breaks slightly and the batter misses, I'd think "Alright, that one worked". I guess it just depends on what angle you're looking at it from.