The fact that the iPad does not have a back button is the stupidest thing ever.
The back button has a fundamental flaw: You don’t know what you’re going back to. It could be anything. That’s user hostile behavior.
The way iOS handles this is better, and gives more clarity. You understand exactly what’s going on when you click a back button. That’s better for the user, and avoids confusion. If a user is constantly confused by a paradigm, they’re more likely to stop using it.