We choose one button to keep it simple (and quicker to get to market). You can do a lot of things with just one button, just look at the single button on the iPhone! For example, you can do two actions, like click and click-hold.
I've experimented with using a single button (a Griffin Powermate, actually) to control all of my electronics: one tap toggles the lights, three taps changes lighting scenes, press and hold/five taps turns the projector on or off, eight taps toggles "party mode," ... I'm quite convinced that multiple buttons would be better :).
