Ron,
sorry to be a bit late on this but I had to think a bit about this one.
So here goes
Bonsai-
Requires a lot of craft skill, artistic talent (or an amazing amount of copying skill
) and an understanding of horticulture to achieve a convincing result. Couple this with the dogged persistence of trees to refuse to bud where you want, refusal to bend as much as you want ( followed by the ominous crack) and the reliance on growing conditions, soil mixtures, fertilising and watering routines, etc and the fact that a bonsai will require life long attendance and maintenace to keep it in shape. Mistakes take a long time to correct and may leave lasting scars that mar the final image.
Painting:
Requires craft skill and artistic talent (again just plain old copying skill will do) in order to portray a 3 dimensional object in a 2 dimensional medium. The desired image can be achieved in a relatively short time and does not need refinement once completed. "Artisic License" is easily employed to alter the image of the original object.
Sculpture:
Requires craft skill and artistic talent (or copying skill). A 3 d model of a 3 d object should be easily achieved and once completed needs no further refinement. "Artisic License" is easily employed to alter the image of the original object.
As to the principles, to portray a realistic image of a bonsai, the priciples of bonsai styling need to be applied to all three artforms. It is what makes a bonsai a bonsai.
A picture or sculpture of a bonsai with crossing branches, inverse taper or lacking nebari would look as odd as a real tree with these faults. I would however be much easier to correct these faults in a painting or sculpture than on a growing tree.
My two pennys worth
Mike