DOF is directly related to sensor size (I'm not sure about film size so I can't comment on film size and DOF effects) the bigger the sensor, the smaller the DOF will be at any given apurture at the same given focal lengths accross the sensor size range. For example, take an average point and shoot camera, taking a picture of friend at say a focal length equal to 85mm, at say an f-stop of f5.6 (average PP), not just the person is in focus, so is the backgrounds due to sensor size. Now say the same setup with a DX DSLR with say a 60mm Macro set at F5.6, now the backgrounds will more then likely look a little out of focus now. Now move up to FX and the backgrounds start getting creamier per say. Look up MF cameras, a potrait shot is probably taken ar f2.8 and looks more like F1.4 on FX cameras due to sensor size being much larger.
Here is a video that was cool to watch comparing a D800 to MF 40mp Hasselblad:
DOF is effected by sensor size due to image circle size or circle of confusion and how that effects light getting to the sensor area.
The DOF calculator info given is due to the fact 55mm on FX is a wider frame and that will "enlarge DOF" due to perspective. All very good learning info. for people (me included) coming from DX to FX. Just trying to help. Not trying to step on toes, just trying to get to an understanding of DOF is all.
It cannot! bokeh is how an out of focus point light source is rendered on the image plane by the lens. It can also be considered as images of the aperture itself. Therefore a nine blade iris diaphragm produces a more pleasing aperture than a seven blade iris because of the more circular shape of the 9 blade iris. The effect is either enhanced or deteriorated by the level of chromatic and spherical aberration correction of the lens
Coming from the D7000, the D800 (or any FX camera) will indeed provide more subject isolation and render the background smoother, when framing the shot in the same way. This is due to the fact that you need to use a longer lens and/or a shorter subject distance to achieve the same framing.
Indeed, that's it. One should always compare settings and results under the condition of 'same angle of view'. DOF calculators don't do that. Another source where it get's explained in detail is: www.123di.com.