I think "open enough to be trusted" is a more accurate description for Red Hat, too. We're definitely not an open company like Gittip, and we do consider various things (like many of our certification tests, for hardware, software and training) to be secrets worth keeping.
When you look at it that way, then a company like GitHub keeping the implementation details of the shiny front end a secret, while open sourcing the back end systems that do the heavy lifting sounds a lot more reasonable, even from an open source purist perspective.