My sense is they all have conceptual models; the question is whether they’ve been consciously planned or have just “evolved” in a haphazard way.

For example, the original iPhone OS didn’t have a list of notifications; now that’s an important feature of the system. How do you allow the user to get to it? Do you offer a visible “notifications” button? Where will that fit, given the real estate constraints of the phone? The “easy” answer is to add another gesture.

As a system accrues more functionality over time, it becomes increasingly more complex. This is to be expected. The issue is that this complexity can make it more difficult to learn the system—especially if lacks obvious affordances.