Apple's toggle button can be pretty confusing, even with the "on" and "off" labels. Are you suppose to turn it on, or is it already on? This is one instance where I think they should have stayed with the checkbox.

Light switches are just as confusing initially- why is up on and down off? Once the convention is established, it becomes more natural.

Plus, since the action is a toggle, it matters less which is which. For the most part I don't care if it's left or right, I just want to toggle it.

Of course radio buttons are explicit, but real estate is also at a premium on an iPhone.

The conventional orientation for light switches is opposite in the US and the UK. But it's not a very strong convention because it doesn't apply to multi-switch arrangements as on staircases.

IIRC they introduced the toggle button for Time Machine in Leopard and it was slightly weird. Why not stick with a checkbox?

Then they released the original iPhone with all it's slidey touchy interaction and it became obvious why they were introducing new UI widgets.