in every halo custom gravity has only ever effected players, so eve when gravity is set to 50% everything is the same except players. not even players in vehicles. in halo 4 i think it should effect everything, players, corpses, scenery, nades, vehicles, EVERYTHING on the ,map.
or we could have 2 options: player gravity, and world gravity.
That would be hilarious. They definitely need to keep player gravity settings though, since it can effect actual gameplay whereas this would just be for messing around.