The company has long grown through accretion, after all, spending billions of dollars over the years on bits and pieces of the online retail universe as it builds towards total domination. The logic behind the acquisitions isn't always immediately clear, but they do tend to fall into a few categories. Here are the main things that end up happening to the businesses Amazon buys:

— Not much. There's a whole constellation of retail sites that Amazon has bought and essentially allowed to continue operating as is, with little to no Amazon branding, and sometimes even with overlapping and competitive business models. Case in point: Zappos.com, which founder Tony Hsieh has run almost completely independently since Amazon purchased the shoe marketplace in 2009 (though they've since found some efficiencies through merging warehouses). There's also Shopbop, which is evolving on its own to sell designer clothes, Quidsi's Daipers.com, the cloth store Fabric.com, and the digital photography review site dpreview.com. And then there's Brilliance Audio, which seems to overlap both with Amazon Publishing and Audible.com, another recent purchase that's building its own partnerships.

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So what's the strategy here? Amazon could want these properties just to keep them out of other big companies' hands, or it could believe that they'll innovate better with their original founders. Finally, it may figure there are communities that will identify more with the "independent" brands than Amazon itself.

— They become pages within Amazonia. That's what happened to the fashion site Endless.com, the early social networking site PlanetAll.com and the book search site Bibliofind.com.

— They get killed outright. Musicfile.com and Accept.com, acquired in 1999, no longer exist in their original form. It's likely that Amazon took whatever patents or data they had and made use of them somehow. And then there's the acqui-hire, when companies are bought for their founders and then powered down, like what happened with the education startup Teachtree.

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— They expand Amazon's reach around the world. Bookpages and Telebook, acquired in 1998, became the company's British and German outlets. Junglee.com is basically Amazon's Indian version, and Joyo.com became Amazon.cn after Amazon bought it in 1994 for $75 million.

— They build out some piece of the Amazon supply chain for digital and physical goods. Take LexCycle, which made an application that allows e-readers to download books in multiple formats; Ivona, which makes voice recognition software that could be used in Kindles; and Booksurge, the company which Amazon required print-on-demand sellers to use until it was sued for anti-competitive behavior (it now operates under the name Createspace). Most recently, Amazon paid $775 million for Kiva Systems, which makes robots for stocking warehouses — a good way to deal with pesky labor problems at its burgeoning network of fulfillment centers.