I vaguely remember something about MS coders already using / to delineate arguments and \ for file paths; when they realized UNIX used \ for that function and they'd have to interoperate over a network, it was already too late.
MS-DOS 1.0 (which did not support directories at all) was already
using / to introduce command-line options. It took this usage
of / from CP/M, which took it from VMS.
