this is not completely true.. when google first released their search application, they were allowed to use an undocumented api (at the time), that detected when you moved your phone from your ear, and was allowed. Not sure if this is the same as a private api, but in general they do reject the use of private api's.
Special exceptions aside, of course. That follows with his other point about big players, which I agree with. They get to do things the little guys don't.
