The Collins Multiscan radar references the terrain database to remove terrain returns from the display ( for the most part ) in auto mode. So unless there's what it considers relevant weather ahead you see a blank screen.
You will paint terrain returns in manual mode though, so Wx deviation is still going to need some SA and common sense. I get the impression that, as you would expect, a lot of this procedure is to cover Boeing and GE's 6 as much as to keep the crew out of trouble! If/when there is another 'drama' it'll be the crews fault, as usual!
