Digital exposure latitude is about more than just the dynamic range of the image sensor.
Half of all the luminosity data in a digital image is in the brightest stop (EV) of exposure. That is the basis for the ETTR - Expose-To-The-Right - concept of controlling digital photo exposure.
To keep it simple assume an image sensor has a dynamic range of just 6 EV (stops), and that the scene photographed has 4096 levels (12-bits) of luminosity.
Note: Most DSLR's output 12-bit or 14-bit digital luminosity numbers from the Analog to Digital (A/D) converter that is between the analog image sensor and the camera's digital image processing computer chip.
With 1/2 of the luminosity data being in the brightest EV of exposure, 2048 levels of luminosity are in that stop of exposure.
The next brightest EV of exposure then has 1/2 of the 2048 or 1024 levels of luminosity, and so on so it looks looe this:
3rd EV - 1/2 of 1024 - or 512 levels
4th - 256 levels
5th - 128 levels
6th - 64 levels
So at some point in the darker regions of the total dynamic range the image sensor is capable of, we have little control of exposure.
We have no control at all once we pass that point that is 1/3 of a stop, because that is the smallest exposure adjustment DSLR cameras have available.
So we expose for the highlights, and let the shadows take care of themselves.
Film is exactly opposite - Expose for the shadows and let the highlights take care of themselves.
http://www.adobe.com/digitalimag/pdfs/linear_gamma.pdf
http://wwwimages.adobe.com/www.adob...ly/prophotographer/pdfs/pscs3_renderprint.pdf