Monday's is the latest example of the online retailer's coy marketing strategy. The third-generation Kindle is the best-selling product in Amazon history, the company claims, but sales figures for the e-reader remain conspicuously absent from the announcement.

The new Kindle, which debuted in July 2010, has now outsold "Harry Potter and the Deathly Hallows (Book 7)," Amazon's previous all-time sales champ. And while some industry watchers have predicted that multi-use tablets like the , Amazon says that's simply not the case.

"We're seeing that many of the people who are buying Kindles also own an LCD tablet. Customers report using their LCD tablets for games, movies, and web browsing and their Kindles for reading sessions," said Amazon founder and CEO Jeff Bezos in a statement.

Certainly, the Kindle's aggressively low price -- the Wi-Fi only model is just $139 -- helped boost its popularity with cost-conscious gift-givers this holiday season. And as Amazon points out, the Kindle's light weight, long battery life, and better readability in direct sunlight (vs. backlit displays) all appeal to book-reading travelers.

So why is Amazon reticent to release sales figures for its e-reader? One possible explanation is that Kindle's numbers pale in comparison to those of the iPad, and Amazon doesn't want to create the impression that it's losing the e-reader battle to Apple.