It Seems Weird How Cheap Amazon Kindles Are - Until You See This Crazy Stat

David McNew/Getty ImagesThese days, you can buy a new Kindle e-reader from Amazon for $49.

Meanwhile, Amazon's Kindle Fire HDX with an 8.9 inch screen costs $379 - much cheaper than a comparable $499 iPad from Apple.

How and why does Amazon charge so little for its gadgets?

Both questions are answered with one single stat.

During a single year, Kindle owners spend, on average, $443 more buying stuff from Amazon than the average Amazon shopper who does not own a Kindle.

Consumer Intelligence Research Partners derived that stat from a survey survey of 300 subjects who made a purchase at Amazon.com in the three-month period ending November 15, 2013.

CIRP estimates that Amazon Kindle device owners spend approximately $1,233 per year buy stuff from Amazon, compared to $790 per year for other customers.

"Another way to look at Kindle Fire and Kindle e-Reader is as a portal to Amazon.com," said Mike Levin of CIRP, in a press release put out to announce the study results (.PDF).

"Kindle Fire provides access to everything Amazon sells, while Kindle e-Reader has become the way that Amazon customers buy books, Amazon's original product line."

Amazon sells Kindles cheap - perhaps at a loss - because it knows getting a device into a customers hands means that customer will spend an extra $4,500 at Amazon over the next 10 years.