That's not what we've been saying. We are repeating what the designers of that particular stem and headset system proscribe. The stem clamp will be unsupported if you leave the spacers above the stem (since the cap can't get down far enough and expand to support the tube from inside). This could lead to the steerer tube cracking. This has zero to do with accident protection for the rider (other than maybe preventing an accident where your steerer snaps off)..