Q: Why are some characters "not allowed" in filenames
A: Because the operating system gives them special significance, like
"\" is a directory delimiter

The "interpretation" of these characters is buried in low level
routines, and is at once "useful" (files beginning with a dot in *nix
are 'invisible'), and also a pain (the basis for rootkits by excluding
files beginning with or containing specific characters) .... from
higher level routines (like DIR)

The OSFI is simply operating at this lower level, allowing it to
read/write without "interference" .... you could probably write a
"patch" to make windows "work"