Equally puzzled and agree the above statement makes no sense. However, to modify your posting slightly; "the steerer and top cap never come in contact in any setup" if the steerer is cut to the correct length or sufficient spacers or stem height are provided above the top of the steerer.

I've never read any manufacturer's instructions that caution against having spacers above the top of the stem. In fact, I've have seen several that recommend cutting the steerer long enough to require a spacer above the stem in the interest of having the stem clamp supported full height.