Interesting. My first thought about Spacedock being a massive antimatter facility, so huge and over-protected due to the dangerous tons of antimatter--why orbit Earth?
If that much antimatter is dangerous (and in ST, it seems to be) why not put Spacedock out near Jupiter, far away from any danger to Earth? Still being in the solar system would be enough to consider it a "home port" even if it isn't directly in Earth orbit.
Or maybe the risk isn't that great. Today we needn't put nuclear power facilities hundreds of miles away from populated areas. Maybe in ST, antimatter facilities also needn't be placed far away from inhabited areas.