Technically they tried to even show the crystal in the current version, the skymap is just so ugly and stretched you can hardly tell. The cyrstal draws it\'s light from the surface world, hence why it not only follows day/night patterns, but seasonal changes. In any case, this works great for a believable day/night system, as the shadows being cast by objects can be expected to remain the same over time.
I do not think stars should be out of the question however, perhaps when the light of the main crystal becomes dimmer at night, you are able to see other smaller crystals shining that also take in light from the world above.