I think Satoshi maybe attempting to inflate the price by providing support to the market with large buys just below market price and smaller buys up front. On Sat, as everyone was expecting a correction there was too much selling pressure to hold it up and he had to let it slide, possibly the 17,00BTC that people keep talking about was sold by another early adopter and he wasn't willing to absorb it.
I saw a couple of times on the way down there would be multiple $100,0000 buys which would quickly vanish when it was clear that price wasn't going to hold. I just don't see anybody risking that kind of money, unless they have a vested interest in bitcoins success and doesn't have as much to loose. Satoshi probably can't sell a large volume at the moment, while keeping his anonymity, he needs to wait for the price to increase and then he can sell of less for higher value. It's also his creation and he with out a doubt wants it succeed.
At $10 I think he finally managed to prevent the price falling through the floor and helped it quickly rebound, confidence is now partially restored as people think we have survived the bubble. He may now on be both sides of the order book trying to peg the price around $20 to provide some semblance of a stable economy (until the next boom). Kind of like a bitcoin guardian angel.