> Would it really have been so terrible to leave the old directory alone and call the new one "Program Files (x64)"?
"Program files" is localized so it's not even "Program files" in all languages. Installers that looked to that folder were doing it wrong anyway and wouldn't work on non-English machines.
"Program Files" isn't localized, at least not on the French version of Windows. Only user content is ("My Documents", "Desktop", ...), and even then, some of them are just links to non-localized directories.
You could, however, change the path of "Program Files" so your point still holds.
You are correct now but Program Files was fully localized in XP and below. In Vista and beyond, it uses junction points to the non-localized names (something I just learned).
"Program files" is localized so it's not even "Program files" in all languages. Installers that looked to that folder were doing it wrong anyway and wouldn't work on non-English machines.