That is all interpretation, though.sunburst is an instantaneous spell. The dispelling of magical darkness is called out because that's a lasting effect of the spell. After the instant flash from sunburst whatever natural light conditions prevailed would resume - including natural darkness if the area was otherwise unlit.
Similarly, some of us think that the logic of fireball calling out the ignition of non-worn, non-carried items is to make it clear that the affect on those objects is not governed by the general rules for damaging objects.