Firstly, I'm not a Windows developer so please forgive any platform specific errors in my response.
If you're talking about runtime libraries that let you interface with an operating system, then for me, that's not an API.
Even if those libraries are available for every language available on the OS. It's still not an API.
An API should be language agnostic. Granted there may be language specific libraries providing wrappers, but the API itself must use an open protocol, making no language requirements. Otherwise it not an API.
