There is no validation on the file system level because file names in NTFS are sequences of arbitrary 16-bit values, similar to how on Unix file systems, file names are sequences of arbitrary 8-bit values. Arguably the situation on Unix is worse, because there the interpretation and validity depends on the current locale.
Totally. These are design choices made by development teams. But as users, we "assume" all are readable until one day we learn that it does not work that way. Until I came across this issue, I assumed them to be all valid, renderable characters.
