Great, maybe they can attempt to implement C99 now 12 years later. I am still required to cripple my C code so it will be accepted by Microsoft's crappy compiler, years after everyone else has moved on. Respecting standards in one place doesn't mean they actually respect standards.
They sell a C++ compiler why should they care about C? C is officially legacy for Microsoft.
http://herbsutter.com/2012/05/03/reader-qa-what-about-vc-and-c99/
There is no law that forces C++ compilers to support plain C. It made sense when the language did not had a big user base.
Plus there are plenty of C compiler vendors for Windows that would happily sell you a compiler.