I had a bunch of stuff quoted, but others have already made those points. Rockspider, you're making a mistake that is very common in beginning physics which is misjudging the frame of reference of the system under discussion. In your rocket-ship example, the only two things in the system are the rocket and the ship. Exhaust leaves the system and transfers force to it in the process of departure. The speed of all of it is irrelevant. Force is what matters, and every single atom of exhaust pushes on the rocket with the same amount of force as it leaves the system. As force is applied to a constant mass, it accelerates, gaining speed from the point of view of an observer outside the system. But the rocket engine and the ship still have zero relative velocity (being attached together) while the exhaust continues to push outward just as hard, forever.
But that's just the real science. In the game, the limits are set for playability and balance.
ETA:
I typed the above while you were typing this. Not piling on...