I'd rather say I am amazed they get anyone great working for them because it really is clearly and painfully obvious that almost everyone would rather work for Google, Facebook or Microsoft regarding machine learning.
Have first hand knowledge of salaries. Amazon offers 30-50% less than other top tech companies for machine learning. There is literally no silver lining or upside as far as I can tell.
In that context, it does not matter if Amazon pays more than <other job> in <other industry> or treats employees better than <other company> in <other industry>.