The thing thing about space sims is don't have as many complex things to keep track of or render. As things get complicated, the game turns into an interactive screensaver (like many we've seen recently). Effects (like an explosion or weapons fire) can be advanced, and ship models could be detailed to an extent (too many external details are believably unlikely). Making the game MMO definently restricts the number of random artifacts you can place in space and perform collission detection on while keeping it playable on a slower connection. All in all, MMO space sims are about as advanced as they can get without sacrificing players on modems. (Though this is all ironic for my to be saying since I'd like to eventually turn
my game into 3D.