Tim Cook revealed on Tuesday at the AllThingsD: D11 conference that Apple has now sold more than 13 million second-generation Apple TV devices. Even more impressive, the CEO noted that roughly half of those devices were sold in the past year alone. Philip Elmer-DeWitt of Fortune crunched the numbers and found that Apple controls more than half of the digital media receiver market. Not including dedicated gaming systems such as the PlayStation 3 and Xbox 360, Apple TV has a 71% share of the market. The popular Roku box has sold more than 5 million units, giving it a 27% share of the market, and the Boxee Box sold about 200,000 units, for a 1% share, before it was discontinued last summer.