E-book sales are up 43%, but that's still a 'slowdown'

• E-book sales have increased a total of 4%2C456%25 since 2008
• Hardcovers are still more popular than e-books%2C though%2C with 557 million sold last year
• Publishers and retailers are split%3A Will e-books continue to rise%2C or will it level out%3F

After three years of triple-digit increases, the number of e-books sold last year grew by only 43%.

And that's enough of a difference in the annual growth rate to have publishers talking about an e-book "slowdown," even as digital books remain the fastest-growing part of the market. They now account for about 20% of all book sales reported by publishers.

Preliminary data from the annual BookStats study, released Wednesday by the Association of American Publishers and the Book Industry Study Group, shows that 457 million e-books were sold last year. That's up 4456% since 2008, when just 10 million e-books were sold.

But it's still fewer than the 557 million hardcovers sold last year. (Paperback numbers are incomplete.)

Interpretations vary:

• The "slowdown reflects a marketplace that is maturing with multiple formats — digital and print," says Michael Pietsch, CEO of the Hachette Book Group. He adds, "In all the talk about e-books, we often lose track of the fact that more than three out of four books sold in the U.S. are still printed ones."

• "We've just reached a point of natural resistance — there are people who really prefer to read on paper even if it is cheaper, faster and easier to read on a device," says Mike Shatzkin, a publishing consultant and organizer of the annual Digital Book World conference.

• "We still see a steady transition in reading from to print to digital," says Amazon vice president Russ Grandinetti. He attributes the smaller growth rate to "the law of large numbers. As e-books have grown from practically nothing, you can't expect it to keep doubling every year."

• "Consumers have settled into their book formats of choice," says Barnes & Noble CEO William Lynch. "Physical book sales will have a longer tail than previously anticipated."

• "As iPads and other devices become more versatile and popular, more people are playing games or watching videos, rather than buying and reading e-books," says Michael Norris, an analyst with Simba Information, a market research firm. (A Simba survey found that 48% of iPad owners do not use e-books.)

The BookStats study shows that hardcover sales rose 6% last year; trade paperbacks dropped less than 1%. Figures are not yet available for the cheaper mass-market paperbacks, which are expected to be most affected by the rise of e-books.