You're not convinced? Did you read the judgement of the copyright office in the first post in this thread? They said only source code and audiovisual material (art assets) are copyrightable not game design.
Stardock did not steal SC source code and Stardock did not steal or exactly copy audiovisual material from SC. I agree that red hyperspace looks very similar on the surface, but it is different. Same game design but DIFFERENT art assets. The biggest difference is that SCO hyperspace is isometric not top-down like SC and the second biggest difference is SCO hyperspace shows entire star systems and 3D spaceship models instead of the primitive black dots used in SC. The HUD is also different.
the test is called "Substantial Similarity" (https://en.wikipedia.org/wiki/Substantial_similarity):
Direct evidence of actual copying by a defendant rarely exists, so plaintiffs must often resort to indirectly proving copying. Typically, this is done by first showing that the defendant had access to the plaintiff's work and that the degree of similarity between the two works is so striking or substantial that the similarity could only have been caused by copying, and not, for example, through "coincidence, independent creation, or a prior common source".
There's not a lot of solid case law here, but you can see some previous cases explored over at: http://www.gamasutra.com/view/feature/187385/clone_wars_the_five_most_.php.
You can see from examples like Yeti Town, that completely different art assets, and a different UI layout, wasn't distinct enough. Conversely, Meteors was basically just a modernization of Asteroids, and it was protected.