I'm guessing that there were at least three things at play here:
(1) cultural - as you speculate, different traditions lead to different decisions being made
(2) technology - the Japanese equipment you show are all electric-powered if I recall correctly, while the Zephyrs were diesel-powered. The third photo in your collection is a freight locomotive, kind of contemporaneous to
South Shore #701 - PentaxForums.com
and those two look more similar to each other than to any of the others in your collection
(3) time - the Pioneer Zephyr was built in 1933, at a time when the Burlington was trying to put some life into their passenger operation, so they wanted something that would get attention. It did. This was a time of art deco and "streamline moderne", and that influenced its design. As time went on, operation of these trains led to lessons which influenced later designs. I can't find my photo right now, but the "zephyr" style of locomotive was followed by the "E-3" of 1940; the most noticeable change is that the locomotive is higher, raising the crew to a higher position so they were less vulnerable during collisions.