.. and therein lies the problem ...
some of us are of the view that one should never quite trust the whizz bang gear too much ... I can recall on the 733 without DME/DME after several hours ... having the map show the runway in quite a different position compared to where we knew it was from looking at it on final ... were a chap to cheat and try a letdown on the magenta line without anything updating the position data ... could be embarrassing.