Originally posted by JinDesu It has a shutter. See The Camera Store's video of it - upon activating the shutter button, you see the shutter cut across the sensor.
Take a look at the 1:27 minute mark of the video. Just as he removes the lens, the sensor is fully exposed.
Add static, dust, wind or smoke into the mix, and somebody is going to be kept busy cleaning the sensor.
With proper technique, contamination can be kept to a minimum. Anyway, it is a pre-production model, so who knows.
It one of the trade offs I suppose.