Here's how that would work:
If by some means you were able to build a massive, roughly-spherical, orbiting extermination platform, and decided to put them on sale to various Sith Lords® and Galactic Emperors, you couldn't call it a Death Star, because that name is Trademarked and Copyright to Lucasfilm. (You also couldn't make it look too much like the thing portrayed in the films, but thats another story.)
On the other hand, if you developed some new technology that either made the building of the thing possible (some method of flinging huge quantities of construction material into orbit) or operating (a method of concentrating a massive planet-destroying ray) you certainly could patent those inventions.
Samsung Imperial SpaceShip Building, for instance, couldn't come along, use all the technology you invented without asking for it or paying for it, and then have their lawyers put up a still from the 1977 film and somehow claim "prior art".
Which is kind of what they've done here.