The minimum resolution requirement is a by-product of the game being made with Unity. Lower resolutions may work, but they aren't supported. The most likely occurrence if you choose a lower resolution is you'll get graphics that aren't displayed correctly, like The Vampire100 said. The graphics were designed with a certain resolution in mind, and anything higher than that makes everything tiny, and anything lower than that makes everything big and ugly (Based off what I know of AI War, I'm assuming its the same for SC).
That being said, I don't currently have a copy to test that theory with, so I can't give you a definitive answer. I have forwarded your question to a developer, who might be able to hop on over and give you more information, but I'd like to think that what I've said sums it up pretty well.