Mark,
I think you have it - you must order the universal garage door opener to get the compass. Both are part of the "optional" rearview mirror. Maybe the automatic dimming feature is all part of the optional mirror also - all three features are tied together? It is not clear on the online order site (doesn't even mention the compass). I guess I'll learn what features I have or don't have just by living with the Mini, all part of the experience. I have a friend who recently bought a BMW X1 and he is going through the same experience, even figuring out the same options as the Mini.