SAN FRANCISCO -- Amazon ( AMZN) Chief Executive Jeff Bezos doesn't expect the company's portable wireless reading device to replace physical books, but he allowed for the possibility of the Kindle to one day become a significant part of the online retailer's business.

Speaking at the annual D6 conference in Carlsbad, Calif., hosted by The Wall Street Journal, Bezos declined to specify how many Kindles have been sold by Amazon since their release last fall, but noted that unit sales account for more than 6% of total book sales for the 125,000 titles available on the device.

On Tuesday, Amazon lowered the price of the Kindle to $359 from $399. On Wednesday, Bezos said the move didn't signify that the company would come out with an upgrade anytime soon, according to the All Things Digital Web site.

The speed by which analog books are converted into digital text will largely depend on how quickly the publishing industry can make the transition, Bezos said. The goal of Kindle, he added, is to allow users to seamlessly download books onto the device in 60 seconds or less.

Bezos acknowledged that pursuing initiatives such as e-books and Web services is a new frontier for Amazon, but by sticking to only what it knows, the company would run the risk of becoming outmoded.

As for any concerns that Amazon might have over the macro-economy, Bezos said so far it hasn't been a problem.

The company last month managed to beat Wall Street estimates for the first quarter but analysts were disappointed with its flat operating margins.

On Tuesday, bookstore chain Borders ( BGP) said it was ending its seven-year relationship with Amazon, reverting to its previous model of selling books online on its own.

Borders had partnered up with Amazon in 2001 after failing to turn a profit on the Internet.

Shares of Amazon were recently down 1.3%, or $1.04, to $79.58.