Why jQuery getJSON works ie. with http://picasaweb.google.com/data/feed/api/user/ or 'http://query.yahooapis.com/v1/public/

Question

Why jQuery getJSON or similar calls work with picasweb or yahoo APIs and they do not work with any other url outside the the my page domain?

Answer 1

Same Origin Policy:

In computing, the same origin policy is an important security concept for a number of browser-side programming languages, such as JavaScript. The policy permits scripts running on pages originating from the same site – a combination of scheme, hostname, and port number to access each other's methods and properties with no specific restrictions, but prevents access to most methods and properties across pages on different sites.