I don't think that's necessarily true.

If dying violently was enough on its own, then there would be scads of ghosts floating around, left behind by the war, even if you also discount those brave or unafraid-of-death enough to fight.

Moreover, Hermione's greatest fear (from the Dementor chapters) was dying alone, and Harry was there to assuage that fear. It's possible that that was enough to allow her to pass on, and that Harry's presence was the only reason that she didn't actually become a ghost. Which could have interesting effects on him if he ever found out.

Which doesn't mean that something extra isn't going on.