You're right, of course. I meant mirror (which also has to flip at 12 fps).Agreed - the shutter needed to be robust to move at 12 fps and last 400K cycles, I suspect they made it as quiet as they could...
I wouldn't think the shutter drove the design as much as the mirror mechanism. Shutters have been capable of opening and closing over the frame at 1/8000 sec.
Yep, it's a heavy inertial component. I've never had one fail (always tend to replace cameras before about 70,000 actuations). I wonder whether the drive motor goes or whether parts actually break.