Fire is a ball/fire is a cone qualify as different spells in D&D but they are not different effects. It would be difficult to justify in lore why psionics could do cones but not balls.I should clarify that there are a small handful of pyrokineticts in Starcraft, but it's rare. But a handful of psionists being able to do a bit with fire doesn't mean that a psionist is capable of every fire spell that a wizard has at their disposal. And in 3e psionics, for example, the pyrokineticist was a PrC rather than a base kit of the psion. As to why lightning and electricity, I think that stems from the origins of psionics: i.e., Psi - Electronics.
As for "electronics" that's complete hogwash. It has more to do with blue matching the protoss faction's colour scheme. Down to the Dark Protoss sub-faction making red lightning.