It's not that suprising that no one has run across this before. Stellar manipulation is a late game tech, and the AI doesn't use it very often anyway. Most people don't get that far in a game before abandoning it to try some new data file tweak.
It's also not suprising that Planetary Gravity Shields work in an entire sector. The Black Hole or Nebula preventers are supposed to work in an entire SYSTEM, after all, even if they don't right now.
The ability description is not very clear. It could easily be some "field" effect that covers all planets in a sector, though.
[This message has been edited by Baron Munchausen (edited 06 June 2001).]