Take CATransition as an example.
Why does Google return those results and not learn that I actually need the iOS reference library and is there a way to make it return the proper results for me?
It usually works by adding the ios keyword in the search query, but it's annoying. I generally return to the search results and click the link from the iOS Reference Library, or do another query with ios at the end and this brings me to the needed page, but I would expect the search engine to learn that I am not interested in the Mac OS X Reference.
It's probably too much to expect a search engine to tailor its results to your behavior, too many people use the same computers often without logging out of their Google account for it to be reliable.
However there is a quick fix, just make a slight change in the address bar once you're in the OSX reference.
http://developer.apple.com/library/mac/#documentation/GraphicsImaging/Reference/CATransition_class/Introduction/Introduction.html
Can be switched to http://developer.apple.com/library/ios/#documentation/GraphicsImaging/Reference/CATransition_class/Introduction/Introduction.html
Works for me every time.