Actually it's not. Microsoft started off as a Unix vendor and even though it has a lot of VMS influences the Unix influence definitely shines through.
It's certainly a lot more Unix-like then, say, AS/400 or VSE/ESA. Ever used a thirty-_ONE_ bit operating system? I have. It's not pleasant.
>They have no support for contemporary POSIX/SUS or C standards.
Actually Microsoft Windows does have POSIX/SUS support.
The NT kernel has the ability to support multiple 'userspace personalities'. This is a side effect of it's layered 'Hybrid Microkernel' design with internal APIs and message passing. Originally it only supported the NT userland. Later one, with windows 2000, win32 support was added. POSIX is just yet another 'native' userland API that is supported by Microsoft Windows.
Numerous government entities have POSIX requirements for operating systems.. In order to get contracts with those entities Microsoft must provide a POSIX operating system. Microsoft does this previously through SFU in the past and now through SUA.
One of the options you get for the higher priced versions of Windows Visa and Windows 7 is that they can be effectively a Unix operating system, depending on your specific configuration. Of course nobody gives a flying flick about POSIX so it's being depreciated in Windows 8.
Maybe this will help put the whole 'POSIX' thing into perspective. Maybe not.
If POSIX is all that important then why are not people using native BSD-style user-land that Microsoft offers rather then trying to shoe-horn a Linux environment via third-party win32 binary? (aka Cygwin or other proprietary competitors) The answer, it seems, is that it's a lot easier to ignore POSIX completely if you are aiming for portability.