The original article on which this article is based[1] has an interesting chart of median employee tenure for various companies. Amazon is at the bottom, with the median employee leaving after only one year. Google is not much better, with a median employee staying 1.1 years. In contrast, Microsoft employees stay 4 years and IBM employees 6.4 years.
The chart has the useful footnote that it, "does not account for overall growth in workforce" which penalizes companies with quickly growing headcounts. I'd also guess Amazon's warehouse staff has more churn that a technology company and they are a large portion of the overall workforce there.
I have very little insight into the matter. Just noting some limitations and biases in the data presented. Former employees are probably biased sources of data, too.
Anyway, I've heard it's a tough place to work, but some people thrive on it... nothing beyond what's in the Businessweek article.
Keep in mind that this measures the median tenure of current employees, which significantly biases against companies like Google and Amazon that have done a lot of hiring in the last few years.
A better measure would be the median tenure of employees that left.
[1] http://www.businessweek.com/articles/2013-10-10/jeff-bezos-a...