On the DaVinci the Z-offset is stored by the firmware, it's a specific amount the bed moves down from the Z stop sensor and is accounted for in XYZware (this isn't the same as manually jogging the Z axis).
Other slicers may or may not deal with this issue well. For instance, the start of a print job if sliced by Cura looks like this (only the line that matters shown) G0 F2700 X71.80 Y71.80 Z0.30. Now all of the G0 commands must be changed to G1 to print on DaVinci, but the important part is that last Z0.30 which means the bed will be moved down .3 mm from where the printer thinks that Z home is. Cura then prints a skirt around the object and starts printing. I have the initial layer in Cura set at .3 which is why that number appears.
In XYZware that same command looks like G1 Z0.350 F2700.000 and it will issue a few more movement and a negative extrusion command before it to moves to a spot on the edge of the glass for its priming line and then starts its print. Notice that XYZware moved .35 mm on the Z axis. XYZ apparently decided that initial layer should be .35 since you can't change that setting.
