The hydra ( http://github.com/ory/hydra ) project for example has groups, which allow you to set e.g. an admin group and then assign people to it. I think this helps a lot with managing policies!
The inclusion of boolean logic in the policies is the root cause.
Specifically, having not resources, or not principals and their interaction with the other policies in the account.
The second highest common cause is misunderstanding how the default deny works.
Again, not really an issue with the landon project, but more an observation on how added power (complexity) to access control systems can sometimes make things less secure.
This policy looks reasonable to a casual observer, but actually gives * access to everything in the account. IAM policies are _hard_.