Say you're an Apple key employee. One who is prohibited from trading within so many days prior to the earnings report (because you have insider information). You sit there, note the stock price runup, and say "man, I'd like to sell a few of my shares at $300".
So you talk to your broker, personal financial advisor, etc, and tell them "I want to move 1,000 shares at $300 once the quiet period is over.
Bam, stock price drops temporarily, and then starts to trickle back up. I have no idea how many people are in this category, but I'm sure there are more than a few at Apple.