Why do you only need one button?

Benefits of only one button

Smaller learning curve
Fewer buttons to be confused by
Decreases reliance on confusing contextual menus
Fewer parts to break
Looks more stylish
No games
Less bandwidth required by USB bus, leaving more power for copying music to your iPod Shuffle.
More modifier keys than on a PC (⌥, ⌘)
Because if you Pres Butan, Go.
If it's good enough for Steve, it's good enough for you
Everybody has had one, and one is enough for anybody
Encourages use of keyboard short-cuts
Doomsday devices have only one
It forces software designers to create better user interfaces
Although Apple's mice have one button, multiple buttons are fully supported