I don't think Jackson 'messed up' at all. He most likely knew that the book never mentioned Saruman shooting fireballs (although it also never mentioned that he couldn't, that I remember) but decided to go ahead & have his movie version of Saruman be able to do that. In light of many of Jackson's other changes, this one strikes me as a rather slight & understandable change, as the 'non-book reading' audience would only assume having powers (not just vocal ones) to be a normal trait for a wizard. As for me, I have no real problem with it, I see no reason why it would violate any of Tolkien's set-in-stone writings (feel free to prove me wrong, though) and, as I said before, it seems like a rather minor change to me.
|