The public API you are referring to is a Mac OS X API. You assert that it is alright to transfer the image provided by that API to another device and display it there. This may or may not be the case but in my opinion, you argument could be a non sequitur. Just because one system provides you the means of getting a certain bitmap does not automatically entitle you to use that bitmap somewhere else.

I think you should be allowed to use it and as a fellow developer I dislike the AppStore model as much as the next person. Nevertheless, your argument isn't really logically sound here as far as I'm concerned.