Uh oh, looks like my tech writing career is under threat (so of course I'm posting with a bit of bias here). A wise move on amazon's part though, offload your work on to users who will improve the docs for a couple of reasons: 1. They can add their contributions to their resumes. 2. They use the software and more than likely reference the docs, and so are already stakeholders that desire the content to be correct and…
I find interesting the assumption every comments make that people are "dumb enough to work for free for Amazon if it's openly accessible". To give the possibility to everyone for proposing changes to their documentation doesn't mean EVERYONE will propose changes. It simply means people who have interest in doing so will be able to do it more easily. We can see this like a reduction of the cost of communication for everyone who have interests at a better Amazon's documentation.
To me, it looks like common sense : you won't give money to someone for fixing a comma, because it's not hard and therefore it's not labor. The power of internet is that the work can be split among so many people that the "work" isn't "work" anymore. If it take everyone participating only 5 minutes a day to improve the documentation, then I cannot see how you would remunerate people with money. People can however still point to their github accounts to prove they contributed, and they "earn" reputation instead of money (ala StackOverflow).