I have seen many projects have little bots do things like post to third-party review services or whatever. Many projects use CI tools that have GitHub integration (e.g. travis), Rust's is just rolling their own so they needed their own GitHub integration. We should be lauding GitHub for their willingness to support integration, even if their native tools are a tad lacking.
AFAIK Bors doesn't use any github integration, it behaves as a user (and I'm pretty sure its messages are too complex to go through the statuses API and result in anything other than unreadable garbage)
Bors does have some github integration and it will automatically merge pull requests and I believe it does update the status, but yes, the details of its interactions are by posting normal comments.
