So what are the changes to the current "Der Hochbeinige" since opening in 1975? For a while, the train said "Heidelberg Express" (as seen in the video above rather than "Preussische Staatsbahn", which is currently the only signage.
My only guess as to the removal of the "Der Hochbeinige" signage, aside from possible laziness, is that the American pronunciation sounds very bad, and some people might even mishear it as a racial slur, sadly. However, I think I have only ever heard one or two conductors pronounce "Preussische Staatsbahn" correctly. It's quite a tongue twister vs. "Der Hochbeinige".