If everyone has the same "problem", maybe it is because the keyboard was DESIGNED this way?
The macbook is designed for the optimal user comfort, and I believe the ambient light sensor was coded to adapt to the ambient condition. The keyboard backlight, like the screen brightness, dims in a very-low-light environment, because it is the most comfortable to the eyes. In only moderately low-light condition, keyboard/screen brightness is turned up because the illumination will not be hard on the eyes (user's perception).
Very-Low light: Keyboard and Screen are dimmed
Moderately low light: keyboard is illuminated but turned up
Ample light: Keyboard illumination is turned off
However I'd be suspicious if your keyboard backlight turns completely off in pitch blackness.
BTW your iphone has the exact same behavior. You'll understand why if you try typing a text message in a movie theater with the auto-brightness disabled.