It's not about the ability to write programs, but the ability to write programs that influence your base system in a meaningful way. Yes, you can write programs, but can you write a different /bin/init for your system? I'm not sure you can (either because Apple will not let you, or your lack of ability to do things like setting up a system to be used). Maybe you can, we're wrong about this, and more power to you. But it's quite likely that you can't.