I think people don't expect more realism in a sci-fi RPG that they expect realism in a medieval-fantasy RPG. By "realism" people usually mean "something I can relate to my experience (first-hand or second-hand) of the world we live in". In a medieval fantasy game, this usually means "nobody in its right mind should expect to jump down a 30-foot cliff and keep on running at full pace". In sci-fi it usually means that some basic principles of Newtonian physics will be applied.
Obviously, there's always going to be a part of fiction in science-fiction, but those who enjoy hard sci-fi will look for a game with mechanics a bit closer to what we know of space exploration (or what we think we know of space exploration) than a space-opera RPG with concepts that no-longer have anything to do with science.
Personally, I like the fact that my X-wing needs to bank when turning, or stops moving if let go of the gas pedal. Perhaps the inertia-dampeners are more effective on the z-axis than the y-axis due to propulsion systems? But at that point, whatever techno-babbling explanation I'll come with has little to do with science.
But as much as I like my space-opera, that boardgame looks magnificent...