It is called a vendor providing an API for a platform with useful features implemented, so that one can focus on building solutions to one's problems and not reinvent the wheel. Watch out, the way you said it makes you sound like a free software fanatic/proprietary system hater.

I would seriously consider Obj-C on non-OSX systems if it had a better library available (GNUstep doesn't cut it), but that's a chicken-and-egg problem.