Everyone makes mistakes. The trick is to make mistakes when nobody is looking.Why be difficult when with a bit of effort you can be impossible?Light travels faster than sound. This is why some people appear bright until you hear them speak. Never hit a man with glasses. Hit him with a baseball bat.
I'm assuming you mean birds the can actually fly around int he sky and what not. Well I'm assuming they are not there because Notch hasn't found a particularly useful purpose for them yet? You already get eggs and feathers from chickens. They would more or less be decoration. Which isn't necessarily a bad thing, but there is MUCH more important stuff he should be adding/tweaking in the game before he implements something relatively useless.