It may also be that those reporting on NT and OS/2 development falsely understood the built-in POSIX support as "Unix borrowings". According to Wikipedia,
Windows NT-based operating systems up to Windows 2000 had a POSIX layer built into the operating system, and UNIX Services for Windows provided a UNIX-like operating environment.
The media may have been taken in by the Windows NT "POSIX subsystem" but most developers saw through it as a cynical ploy to allow Microsoft to tick the "POSIX compliant" box required by some government contracts, without actually being usable. The POSIX subsystem was (deliberately?) crippled by being unable (by design) to properly interoperate with the Win32 subsystem and most developers accordingly avoided it like the plague (again writing this from memory of 10+ years ago when we briefly considered using it but opted instead for Win32 subsystem Unix emulation layers).
To paraphrase Dave Cutler, "Microsoft Windows Unix products are a crock". :) Generally, 3rd party Unix toolkits (eg. cygwin) are preferred.