"How do you know that Apple's designers aren't also testing their designs with real world users?"
Having worked there, I can vouch for this. Apple employees (and, most notably, Steve himself) are the real world users they test with. Every important or critical product only ever sees internal testing, but much more important is that the rationale behind Apple's design process is that of an actual designer thinking about solving problems from a user’s own perspective, whereas Google's "design process" is based entirely on trying to solve problems from an engineering perspective.* Often, they take it so far that they only solve engineers' problems, not even general users' problems.
* That's bad because the vast majority of people on this world are not dedicated engineers.
How do you know that Apple's designers aren't also testing their designs with real world users?
I don't think "design vs real world testing of experiments" is a binary choice.