There'd be at least four buttons: the two sticks will double as buttons, and the shoulder scroll wheels will likely be clickable like buttons. I'm guessing they imagine that "most games" can be more or less accommodated with just these inputs (letting them simplify the interface for those games), and for actions that can't be accommodated they've got a haptic touch button option that can mimic traditional controls.
I'd imagine they've overcome some of the major hurdles that have kept them from using touch technology to replace buttons in the past (in particular, that they've hit on a haptic technology that provides the right amount of feedback), or they wouldn't be bothering to try to implement it now.
I'll put it this way:
2D Mario games generally only use two buttons: jump and run/power-up. Those can both be mapped to clickable sticks on the face (we'll call them LS and RS). Done.
Left analog: Move
LS: Power-up
RS: Jump
Zelda games generally use buttons for performing actions (talk, pick up, etc.), attacking (sword), using items, targeting enemies, and using a shield. Actions are generally context-sensitive, and often aren't timing-sensitive. Those can be mapped to a tap on the screen. Players can press the right stick to swing their sword, and the left stick to use an item. The left trigger could still be target, and the right trigger could be shield. The scroll wheels would let people cycle through their inventory easily. And of course the second screen could be used for things like map display while playing on the TV.
Left analog: Move
Right analog: Camera
LS: Use equipped item
RS: Swing sword
L button: Target
R button: Shield
One of the two scroll wheels: Cycle items
Other scroll wheel: Cycle weapons (?)
Tap screen: Talk/pick up/throw/etc.
Not too bad, right?
Metroid (we'll say Prime)
Left analog: Move
Right analog: Aim
LS: Morph Ball
RS: Jump
L button: Target/Scan
R button: Fire
L scroll wheel: Select visor
R scroll wheel: Select weapon
It's really not hard to see how most traditional Nintendo franchises could easily adapt the interface we've seen.
