In the beginning of Blackwell Deception, how is the ghost driving the boat? No other ghost in the series (with the exception of the Countess, who has special powers) has been able to touch solid objects.
Well, Jeremy could still make an actual phone call without a phone and Joey can mess with electronics/blow on stuff, so clearly they're not completely separate from the physical world. It would seem that ghosts have connections to things that were very important to them and retain some control over them. Presumably it's even stronger if that's where they died.