My main reason was for consistency (especially for error messages).  But....I looked around in /var/log, Windows event logs, and a half dozen or so stack overflow discussions.  After all that I'm going to back track here because you're right and there's lots of info for other devs. to support your argument.  I'm removing that section from the docs so please ignore my original comment:

https://github.com/pyfarm/pyfarm-docs/commit/cc77f19b3fb4db1afa68b2043d4a50d17f64fbef

The content of the message still itself matters more than capitalization or even spelling, not that we (or rather I) should be neglecting either of those however.