Okay, let me point this out to you a little simpler: Why is there a shadow on both the left and right sides of the plateaus? Light doesn't do that. Why aren't there shadows on the grass? Light doesn't do that, either. If the edging of the grass is done with the same tone as the shading, what is stopping the viewer from seeing shading as edging? If those are shadows around the plateaus, why are they not varying lengths due to the height of the plateaus? Light doesn't do that.
Here's a quick diagram. Assume that the "sun" size is exact, and the space it occupies is two dimensional, there is no Z-planar difference. This is what they should have done:
Now, this is what they did:
Even more bizarre is the comparison between the shadow of the block atop the higher plateau, and Mario/Luigi's shadow size as well as the para troopa's. Their distance from their respective casting surfaces is not of any great difference. Despite this, the shadow of the block is of identical 2D proportions to a bottom facet of the block. Mario and Luigi should cast a larger shadow based on these observations, and the troopa should cast a much larger shadow.
Additionally, although this is more proper than I truly expect, the darkness of the shadow of any of the objects on screen should be comparable to the shadows cast by the plateaus, or at least the plateau shadows should be
darker, and they should certainly be
larger. What the f is going on.