The problem is that it's not the "Home Button", it's the "Back Button".
I use Android, but I do see the value of the single-button UI. Although it may not be the "get me home ASAP button", it is easy to learn what happens. The only thing you can do with the phone is press that button. That makes it very easy to learn what's going to happen, and it's easy to predict what will happen in the future.
But, it is the home button! It always takes you to a variant of the home screen, and a given app can't change it's behavior. If you click a link out of an email, it doesn't take you back to email, it takes you to the home screen. Just, some random folder on some random page.
I use Android, but I do see the value of the single-button UI. Although it may not be the "get me home ASAP button", it is easy to learn what happens. The only thing you can do with the phone is press that button. That makes it very easy to learn what's going to happen, and it's easy to predict what will happen in the future.