Ex-AWS employee here. I tend to disagree with the above statement. Though, their retention numbers are pathetic to say the least, but it was an awesome place to work and learn and most of the people who do leave tend to go to the high flying places.
Ex-Amazonian here also. Sadly, Amazon looks great on your resume, it's still considered in the "AAA" tier of tech employers, standing side by side with the likes of Google, Facebook, etc.
Realistically I'd argue it's more on the high end of the "B" tier, but that's neither here nor there.
Amazon's attrition rate is insane. Not high, insane. This should tell you a lot about what it's like to work there. I too learned a lot, and it continues to pay dividends on my resume, so I guess that's how they get away with it.