Amazon has grown dramatically and a large part of it can be attributed to launching Amazon marketplace in 2000 which allows third party retailers to sell their products through Amazon. Over 50% of sales on Amazon are now sold through third parties. Amazon's focus is lowering prices to get consumers to buy more. In turn, consumers become more frequent shoppers on Amazon for all their purchases. With more volume, they make more money and more capital.
NBC News' article "Amazon Is Hungry and It’s Coming for Your Cable Channels" highlighted that Amazon has been buying small TV stations in efforts to eventually dominate television. Amazon seems to be using the same strategy that it used with books. Using cheaper distribution (duh, the internet), they are going after the long tail content of television now.