Amazon absolutely strip-mined open source.
In 2001-2006 Amazon was all built on open source and had ditched HP and Digital Unix for Linux, RedHat, Apache, Xen, etc.
It was abusively hard to contribute back to open source projects, including the Linux kernel, and you had to get extensive signoff and review to ensure that you weren't giving away any IP with your lock order bugfix or whatever. There were also constant reminders and threats to not engage in open source discussion in any way that could leak company IP which created an atmosphere where it was much easier to just not participate at all. It was definitely very easy to pull open source into the company and very, very difficult to participate going the other direction.