I've always had an atypical (read: not traditionally competitive) background, both for schools and jobs. As a result, I've found universities and firms that are willing to take a chance on me the best. They are great for me because the tacit agreement is "I know I don't meet the traditional standards, but I'll work hard to prove I'm worth it. And if I'm not, I know you'll fire me." No one ever says it, but it's the strategic system that underlies this.
In short, Amazon offered me a job and a salary no other tech company would have. Not even close. I've had to work nights and weekends not on Amazon, but just on teaching myself the tech to do my job (I'm a data scientist who could barely code when I started). And I'm not doing bad. I'm not a genius, but I'm valuable enough. Once I get all my stock and a promotion, I might look at a 40-hour type company. On the other hand, my team is pretty fun, so I don't know.
I can't speak on everyone at the company, but the campus is basically empty at the times I leave at 7-8 (which isn't often and usually happens when I show up at 11-12). My own building is 95% cleared out by 6pm on a daily basis.
Not saying what you hear isn't true, but it's definitely appears to be the exception rather than the rule from my experience.
All the people I know at Amazon in Seattle consistently get home after 7pm most nights, and a handful of those people come in on the weekends for 10 to 12hrs to fix mundane bugs that aren't in need of immediate fixing. Amazon's high pressure work culture encourages this terrible practice of burning the candle from both ends, but Amazon definitely doesn't create quality products on the first try in part due to this.