The problem with 12MP on the D3/D700 was partly with the very aggressive AA filter. The camera, beautiful as it was, did not roll off in the high frequencies gracefully. This was partly due to the facts of scale as well. 12MP with AA is not quite enough to render details of hair and skin in a medium portrait. The 24/36MP sensors, after being downsampled to 12MP, supply a level of high frequency detail that the native 12MP sensor could not. The 16MP sensor is almost enough, but not quite.