Even if Amazon.com (NASDAQ:AMZN) seems to be doing just fine as it grows its category offerings organically, it's never beyond making the timely acquisition. This morning finds the world's leading online retailer acquiring AbeBooks, an online marketplace for used, rare, and out-of-print books.

AbeBooks is a Canadian heavy in bookselling. It's leaned on by thousands of independent retailers, who have bumped up its  listings to a whopping 110 million books.

Despite Amazon's recent initiatives in literary downloads -- either aurally through its recent acquisition of Audible, or visually through its proprietary Kindle e-book reader -- Amazon knows that it can't lose its old-school street cred. Hooking up readers with obscure titles is part of the game. Amazon is no stranger there, but it has typically leaned on Alibris -- which also powers the used-book marketplace for real-world chains like Books-A-Million (NASDAQ:BAMM) and the online traders at eBay's (NASDAQ:EBAY) Half.com -- or its growing pool of third-party sellers. Snapping up AbeBooks will give Amazon a little more say in this niche.

Amazon didn't need to buy AbeBooks, just as it didn't need to purchase Audible, audiobook publisher Brilliance Audio, or on-demand book publisher BookSurge. Amazon has the brain, brawn, and billfold to make a splash on its own in any of these specialty areas. However, it's more attractive to acquire an established pioneer, because it simultaneously gets Amazon up to speed in the niche and eliminates one competitor.

Amazon had no problem with launching its own virtual boutique for high-end shoes and handbags with Endless.com two years ago, but it found it easier to make a splash in the custom-cut fabrics segment by picking up Fabric.com this summer.

Organic growth plus tactical acquisitions make Amazon the undisputed e-tail champ. It's in the book. Which book? Beats me, but I'm sure that if you scour the 110 million titles on AbeBooks something will come up.

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Longtime Fool contributor Rick Munarriz wonders if Amazon is buying Abe to move higher in the alphabetical listings. He is part of the Rule Breakers newsletter research team, seeking out tomorrow's ultimate growth stocks a day early. He does not own shares in any of the companies in this story. The Fool has a disclosure policy.