As Nat says, APIs are not open source software. The data is not free (as in freedom, not as in beer). You depend on ongoing access to an API at your own risk.
See also a Nov 2005 post where I, after talking with Rael Dornfest, said:
I keep hearing people talk about [APIs] as if companies are creating web services because they just dream of setting all their data free.
Sorry, folks, that isn't the reason.
Companies offer web services to get free ideas, exploit free R&D, and discover promising talent.
That's why the APIs are crippled with restrictions like no more than N hits a day, no commercial use, and no uptime or quality guarantees.
[Companies] offer the APIs so people can build clever toys, the best of which the company will grab -- thank you very much -- and develop further on their own.