Sometimes I go to your site just to relax. Your work is killer bee.
The easiest way for me to think about DOF and D100 is relative to the film plane. For the same image size (not picture size) in the final product from a D100 shot and a 35mm shot, the depth of field will be exactly the same with the same lens and exposure values. If you want the math, see Manual of Photography, 13th. But then there is that pesky crop factor. Because we relate everything to the 24x36 frame size, we expect to magnify the image from the D100 about 1.5 times as much as the 35mm image during post recording processing. The larger the final product, the less tolerate is our eye to out of focus points. Enter circle of confusion. That's why DOF calculations for the D100 use values that are ~2/3 (the reciprocal of 1.5) of the 35mm counterparts. See the excellant Nikonians DOF pages for example, where for 35mm DOF c=.025 and for DSLRs c=.016. When I read posts from D100 users that think the images are soft, I wonder whether it is a DOF issue. DOF is the area that appears in focus. It isn't really a 75mm shot, it's a 1.5 blow up of a 50mm shot. Sure it looks a little softer that a shot from a 75mm lens on a 35mm camera.