I think if the thing goes down, you've had it anyway. The crash position is just designed to give you something interesting to do with the last few seconds of your life.
The safest way to sit is facing the back of the aircraft, but airlines don't implement that because people don't like facing backwards.
Also it sends out the wrong message - ie 'We've got you facing the best way, because there's a possibility we might crash'.
No-one wants to be reminded of that possibility.