It's pretty natural and rational, I think - Amazon rankings update every hour, and are better indicators of long-term success relative to other titles. Likewise

It's pretty natural and rational, I think - Amazon rankings update every hour, and are better indicators of long-term success relative to other titles. Likewise, Amazon's bestseller lists target smaller categories, which is more useful than the broader NYT lists. You just have to filter out the random turbulence in rankings when new titles come out.