Amazon.com (Nasdaq: AMZN) now sells more e-books than hardcover books. That was the company's headline yesterday, designed to shock a few folks, and that it did. But let's look a little deeper at the press release and see exactly what it's saying -- and what it's not saying.

The good
First, Amazon says the Kindle's sales growth rate has tripled since it lowered the price of the basic unit to $189 a few weeks ago. CEO Jeff Bezos calls this a "tipping point," and it does seem pretty impressive considering the e-reading device has already been Amazon's No. 1 seller for two years in a row.

As for actual e-book sales, Amazon says it has sold 143 Kindle books for every 100 hardcover books over the past three months, with the gap increasing in the past month to 180 vs. 100. Free Kindle books (and there are 1.8 million of them) are not counted in the calculations.

So all of that sounds great, and there's no doubt that e-books are continuing to take market share from traditional channels. There's also little doubt that Amazon is the major player in the industry, with roughly 90% market share. A lot of this self-aggrandizing is probably designed to remind folks that despite the wild success of Apple's (Nasdaq: AAPL) iPad tablet, Amazon is still at the center of the e-book universe. With more than 630,000 e-titles, and support for Apple and Microsoft (Nasdaq: MSFT) computing platforms as well as apps for Google (Nasdaq: GOOG) Android phones, the iPhone, and Research In Motion's (Nasdaq: RIMM) BlackBerry, it has an envious reach.

The missing
And yet, Amazon has always been a little too secretive about actual sales figures. You'll note the talk of tripling Kindle sales growth and 143 e-books for every 100 hardcovers sold, but no actual figures. You'll also notice we're only talking about hardcover books here, and not paperbacks. (The New York Times says "paperback sales are thought to still outnumber e-books.") Why not tell us the entire story?

Oh well. The company reports its second-quarter results after market close today on Thursday, so maybe we'll get another chapter of this fascinating e-read then.