Interesting, that has some implications for the placement of asteroids in level design. For example, in Return To Fluffy Land the first asteroid is at (0,0) and the last asteroid is way way down in the southeast - the other asteroids extend in a curvy line between these two points. But if the quad tree always extends outwards from the origin, I could potentially have made the game use 1 size smaller of quad tree by placing the asteroids around the origin instead of starting there and working outwards in one direction. That might mean the game runs faster on slow machines.. :>
Also, it means that by placing asteroids around the origin you can have a great area in which asteroids are allowed to be placed, rather than only using a single quadrant like in RTFL.