It all makes quite perfect sense up to this. The only reason I can see for this is that a smaller frame will be an ounce or two lighter. Not a concern if you're not a racer, or unless you're so old that you're taking body shrinkage into account. My philosophy is to aim for the middle of the range that you feel comfortable on. My thinking is that a 140 mm stem on 52 cm frame looks ridiculous, as does a seatpost that pops up a foot above the top tube. Similarly, a 70mm stem on a 59cm frame, and 3/4" of seatpost showing looks almost as foolish - not to mention, a frame in the middle of the ideal range can be much more easily adapted if your riding posture evolves.