(This kind of comment always elicits current Amazon engineers who disagree because they haven't personally experienced this. To them, I say: Stay at Amazon long enough and it /will/ happen to you. To those currently in the grinder: I hit the eject button at L6 and found a much better gig; it gets better!)
I worked a short contract there and I've seen the 'meatgrinder' bit. I joked (not really joking) with my fellow contractors that maybe the reason they walk four abreast is shell-shock, not arrogance. A couple days a week we went to lunch in a daze.
It's clear there's not enough quality control in their 'culture', by almost an order of magnitude. I've known two different people who quit after less than 2 weeks. One after being called on Sunday asking why he wasn't at work. On his second fucking week at the company.