According to a breathless press release, the Kindle ereader is the "#1 bestselling product across all product categories on Amazon." That means it sold more than the iPod Touch. More than the Wii. More than Going Rogue. How? It's easy!
Step 1: Market a device for two whole years
Step 2: Issue a price drop a few months before the holiday season
Step 3: Remain the exclusive retailer for said device
Step 4: Profit! (To an extent that is completely and intentionally unclear to everyone!)