A sidenote in the article, but I'd like to know why people think that Amazon treats books as a loss-leader... Last I checked in tech news, it was the common ass

A sidenote in the article, but I'd like to know why people think that Amazon treats books as a loss-leader... Last I checked in tech news, it was the common assumption that Amazon retail in general has razor-thin margins or might even be losing money, but AWS was making money hand over fist.