I think it comes down to the difference between eye lines and distance more than anything like the camera's placement above or below the screen. With a laptop any location the difference between looking at screen and camera is pretty drastic because it's pretty close to the user. In a conference room people are generally much farther away and smaller so it's harder to see the difference between looking at the screen and the camera.
Any given person in the other room is generally small enough on the screen that them looking at the screen instead of the camera is fine. But I'm not sure if a more overhead angle would be as good.