The price drop is Sony's way of getting rid of their old inventory.
They originally planned to sell two different consoles... the 40 GB version and the 60 GB version.
The 40 GB version was $500 and the 60 GB version was $600.
They decided to focus on just one console. So, they stopped producing the 40 GB version. All that was left was the 60 GB version. That's to be expected since people like getting something that offers more anyway.
Now, they have a 80 GB version and no longer need to produce the 60 GB version. So, they reduce the price of the 60 GB version to $500... to make them sell faster. The new version is the 80 GB version which is now $600.
So, basically... there was no real "OMG! There's an awesome price drop for the Playstation 3! Yay!" It's more of... "Okay, the 60 GB version is now crap. You can have it for $500 instead. The 80 GB version is now $600. Enjoy."