It's kind of funny, actually. Back in the old days (we're talking the first years of the 1980s), controllers had become about as complex as they are now. They featured the first iterations of analog sticks in the form of joysticks and disc controllers, they had numeric keypads on them, there were fire buttons galore, and overall they just kept getting more and more ridiculously complex. It was pretty much topped by the Intellivision, which had a total of 17 buttons. And this was an era of one-handed game controllers, to boot! This all started with a simple 1-button controller from Atari, which was easy to use, and developed into ridiculousness as everybody tried to outdo each other.
Then the NES came along, with only 4 buttons and a D-pad. It introduced the idea of an easy-to-use two-handed controller which anybody could handle. But again, the "better than you" thing started again, and we ended up with some of the most ridiculously complex controllers ever. Once again, 17 buttons is a very normal thing to find, even though a well-designed game needs no more than 4.
So we now have the Wii, taking away buttons again (down to 7 plus 1 d-pad) and returning to one-handed controls. But more significantly is the addition of motion controls, which adds a whole new dimension of control which requires no button presses and can potentially be entirely intuitive (something a button cannot be). In time, Wiimote knockoffs will come out with more buttons and more precise motion controls, of course. But probably not from Nintendo. I get the impression that they've had their lot of the whole "bigger and better" race. Whatever they bring out next, don't expect it to have more buttons than the Wiimote...
