Nice question! It can be any of the reasons you mentioned. In all cases you have to set points around the area you want to fill in such a way that you follow the lines of the clipart. In some software you can use those points for filling stitches and outline, in others, like mine, you have to trace them twice, for the filling and the outline. And that can cause (minor) gaps. So it is a matter of accuracy and patience to get it right. As a filling stitch can contract a bit, which the software does not show, it's a matter of experience how much you trace the outline inside the filling, or - second method - place them exactly in the same spot and set up "compensation", which makes the filling a bit wider. This manual punching takes a lot of time. Having the software create a design automatically (autopunching) is quicker but the results need a lot of adjustment. How much depends on the quality of the software; the mathematics vary considerably in the various brands.
Jump stitches have a lot to do with the placement of different colours and the continuity of a design. Those princesses were awful for instance. And here again experience can play a huge part: what pieces to digitize first and connect with single stitches to be covered by the next colour. So you see, it's the ability of the digitizer and the quality of the program he or she uses.
Thanks for this answer, it makes one realise how much work and effort is required in digitising
I agree, I am not a digitizer yet, & maybe never will be, but I sure would like to try!
Thank you for explaining!! when i tried the out line was a good mm or so off on the whole one side.. i tried again but still off,,, so i decided it was not for me... so i commend all you digitizers that have the patience and skill!! thank you