[B Knotts]

Because they are not the same thing, and you don’t interact with them the same way. That is what some people don’t seem to grasp.

What you end up with when you try to unify the interface is a single interface which doesn’t work very well on some or all of the devices on which it is placed.

See: Windows CE, Windows Mobile, etc.

Apple generally has it right: one interface for smartphones and tablets (with some differences even between those two), and a pretty-much entirely different interface for desktop and laptop computers. No one has an especially hard time figuring it out.

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Apple generally has it right: one interface for smartphones and tablets

Except that, even Apple is trying to unify their different devices to work the same way, and to do that, they need to make the UIs look and act the same.

Simplicity is what Apple and Windows have been trying to achieve with their devices, and with their OSes. Heck, even the old Mac OS is in danger of being replaced with iOS, since, in order to achieve sameness across all devices, it would be more easily achieved if only one OS controlled all of the form-factors.

Windows 8 is intended to be "one" OS, even if the underlying code and the underlying hardware and device sizes are all quite different.

The goal of simplicity and sameness is all about the users, and the user doesn't need to have to learn or re-learn a new way of doing things simply because of the different sizes of the devices. There is absolutely no reason that the UI needs to look or be different between all devices. In fact, the UI for all devices and all makes should be the same, and that should include Android and iOS and Windows. Let the battle occur with the applications and the hardware capabilities. If all browsers look basically the same, why can't the UIs for all devices and all makes?