Your logic about the metal pin extending thru and being a good conductor of heat is sound logic. I think the problem is that for some people the metal pin is a double edged sword. It conducts heat well and can keep the nipple thawed if the water is being heated, but for people with frigid temps, the metal pin also can conduct the cold into the container from the outside air. Yeah, science tells us that heat flows from hot areas to cold areas (fast/excited atoms exciting the slower atoms next to them, warming them up), but I think the long metal pin still can be both good and bad depending on how extreme the temperatures you are dealing with are.
I wish I could find it......I swear I saw a photo that showed ice forming on the INSIDE of a water bucket, all around the vertical nipple where it extended on the inside of the bucket. Like a little submerged iceberg inside the bottom of the water filled bucket. Liquid water all around it, but frozen nipple.
I am on team horizontal, but I don't hate on the vertical people. Unless you have leaky verticals. Then I don't have any sympathy. Haha.
EDIT: I tried to Google for an image. I can tell you that "frozen vertical nipple" does not produce the correct image results. Hahaha.