Volume and sleep buttons have nothing to do with UI input. Do you type an email by using the power button on your Mac? No. So that's a bad comparison.
Console gaming, and gaming in general, makes almost no sense without physical buttons. That's why the Wii U tablet has a full button layout, why Nintendo sells "Pro Controllers" for the Wii U, and why the majority of iOS games are still very casual. It's extremely hard to play a reasonably-paced game without the indirect aspect of feeling physical buttons.
Unless you're suggesting Nintendo go the casual route and release a bunch of endless-runners and such...
I think you misunderstand me... I was simply trying to illustrate that Apple is not button free as you indicated, but that instead Apple carefully considers where they utilize buttons and their intended purpose. I don't think any less consideration is taken by Microsoft, Sony, Nintendo when they design their controllers. My phone is not a gaming specific device so it doesn't need gaming specific buttons, but I can get accessory game controllers for it if I want.
I'm not at all suggesting that a Nintendo console should be just for casual gaming or be as minimalist as an iPhone in terms of buttons. Nor do I think if Apple had a gaming focused device that Apple would have so few UI/Game interaction related buttons. I think Apple would evaluate the needs/wants of the particular device they are creating and design a controller accordingly. A standard Wii-Mote has only 7 buttons used for game play
(counting d pad as one button, and not counting home, sync or power buttons) compared to an xbox 360 controller with 13 buttons
(counting d pad as 1, joysticks as 1 each, not counting the guide button or the connect/sync button) Yet I and many other people still enjoy a good many games with what could be considered a relatively minimalist controller, and for other games where I may need more controls I attach a extra controller like a classic, pro or nunchuck, etc... Apple need not rely on just a single controller.
I actually think a possibility for the AppleTV
(or other device IF Apple were to get into the console business..which I doubt) would be for Apple to Utilize iPod's or iPhones, with a gaming controller attachment. That would allow for a nice multi-touch screen, with added buttons and controls that we would all expect to see on a gaming controller, and provide a healthy 3rd party market for attachments. Though I would have some concern on how the ergonomics of such a layout, but it probably wouldn't be much different than the Wii U gamepad I suppose.