Bill, don't you think considering a 10 f-stop DR in a 12-bit RAW based camera is a bit too optimistic? if we assume linear behaviour of the sensor into this usable DR, the entire 10th lowest f-stop would be codified in just 4 different tone non-interpolated levels. I think that's too poor even if noise is not present in such deep shadows, isn't it?
0EV: 2048 levels, 2048..4095
-1EV: 1024 levels, 1024..2047
-2EV: 512 levels, 512..1023
-3EV: 256 levels, 256..511
-4EV: 128 levels, 128..255
-5EV: 64 levels, 64..127
-6EV: 32 levels, 32..63
-7EV: 16 levels, 16..31
-8EV: 8 levels, 8..15
-9EV: 4 levels, 4..7
-10EV: 2 levels, 2..3
-11EV: 1 level, 1
The only thing I can think for reaching such a figure (10 f-stops DR) is to consider a non-linear low end of the response curve of the sensor as a usable range that could include more than 4 effective levels to codify degrees of lightness (of course being these levels "stolen" from upper f-stops, -8EV and up).
And in any case he is using a 16-bit reference, with which I don't agree as those new levels appearing in the 16-bit range and filling it, are purely interpolated. Real captured levels are in a 12-bit range, and only 4 different of them represent the whole 10th f-stop.
As Ray pointed out, calculation of dynamic range of a photograph is not exact, and the floor may be affected by posterization as well as noise. How many levels are needed in the darkest zone is somewhat arbitrary, but 4 levels is probably not sufficient. I think Roger was using a noise floor.
Norman Koren's Imatest allows calculation of dynamic range associated with varying levels of quality. Here is one such test for my Nikon D200 (which has more noise than the Canon 1D M2), and a low quality image with a dynamic range of 10.2 f/stops is obtained. Again, this is using noise as the floor. Norman agrees that the darkest zone should have 8 levels, which would limit DR to 9 stops with a 12 bit image.
I would think that the new Canon 1D MIII with its lower noise and a 14 bit AD converter should be able to get 10 stops of DR easily.