If we remove the scroll wheel, there's another rubber seal on the underside of it (all of these seals are between the gap you see and the camera for those who are disoriented a bit).
http://www.pbase.com/rcicala/image/150353835.jpg
Now if we flip the button assembly over and remove the center tilt button you see orange circuit board material that's sandwiched in the tilt button to trigger the sensors. Note the scroll wheel it fits into behind it: there's only black plastic and rubber behind the wheel. What you're seeing in that gap is the edge of the tilt-wheel circuit board. Behind it would be only black plastic and black rubber gaskets.
http://www.pbase.com/rcicala/image/150353836.jpg
A close up of that.
http://www.pbase.com/rcicala/image/150353837.jpg
You can't really tell, but just inside that edge of circuit board material the actual circuitry is sealed in the button's plastic. Water can't get inside there, nor can it get past the seals in the outer button into the camera.
While the 6D isn't officially weather sealed (not that weather sealing is any guarantee of anything at all), this looks very water resistant to me.
Lesson learned (to Canon): Don't leave any part that looks like circuitry exposed as it can cause some trusting issue.
(And believe me, I'm sure there will still be people who don't get to learn about this thread and the question will pop up here and there. Even for those who read this, some will still have doubt.)
I don't know you but thanks for doing this. I feel better about my 6D. Not that I was planning on taking it out in the rain anytime soon but it is good to know they put some thought into the design. +1 for the 6D
