Actually, I think I remember them starting to mentioning in that book that Ginny is getting FREAKISHLY good at witchcraft. But that always translates in the movies as BLOW SHIT UP. Remember Malfoy and Harry's duel? Every single spell sent someone flying. Remember Harry's "Expelliarmus" on Snape in the third movie THROWING HIM against the wall? same thing. Movie-Power = Explosions or flinging people.