Because `QWORD` is not defined in any file included by CPython. The main file for basic sized type definition in Windows is:

    basetsd.h: Type definitions for the basic sized types.

which contains the definition of `DWORD64`: `typedef unsigned __int64 DWORD64, *PDWORD64;`
but no reference to `QWORD`. Furthemore the code did not compile with the use of `QWORD`.
So, I am pretty sure it is not defined by the standard includes

Other people complain in your link:

    > "Apparently, QWORD isn't defined in any of the windows header files for MSVC 2010."

Finally, the only files where I could find a typedef for `QWORD` are:

    * Include\shared\Sspi.h (Security Support Provider Interface. Prototypes and structure definitions)
    * Include\um\WinDNS.h (Domain Name System (DNS). DNS definitions and DNS API.)
    * Include\um\wmcodecdsp.h (COM interface -> generated code)
    * Include\um\wmnetsourcecreator.h (COM interface -> generated code)
    * Include\um\wmnetsourcecreator.idl (MIDL Interface Definition File)
    * Include\um\wmsdkidl.h (COM interface -> generated code)
    * Include\um\wmsdkidl.idl (MIDL Interface Definition File)
    * Include\um\mfobjects.h (COM interface -> generated code)
    * Include\um\Mfobjects.idl (MIDL Interface Definition File)


It seems to be in pretty obscure files that should not be included by CPython (In my opinion)