That's because most of the people who buy apple stocks look at more than the title and possibly quick description of what was really a situation that was more complicated than you guys think it is. As in... it's not "durrr, STEVE JOBS QUIT!" it's more like "Steve Jobs is passing the torch to someone he finds very good at what he does, someone who Jobs thinks will be very beneficial for the company." and to make things more complicated (for your guys' brains), Steve Jobs is still chairman.
Now.... why would people who OWN these stocks not look into these things and see that Steve Jobs even told the investors not to freak out with legitimate reasons?
They.. are not like you guys, which is why the stock hasn't taken a big hit.