Okay. Maybe I exaggerated. Maybe it is an overstatement to say that substantially there is no difference between the magic in Harry Potter and the magic in The Chronicles of Narnia and The Lord of the Rings. Granted, children learning to read tea-leaves in a divination class smells of the occult more than Aslan being resurrected by deeper magic from before the dawn of time (to take perhaps one of the worst examples in Harry Potter and compare it with the best example in Narnia!). But I was trying to make a point - namely, that magic and witchcraft are standard fare in fantasy stories and that people tend to uncritically accept them in C. S. Lewis or J. R. R. Tolkien (because they were Christians, I suppose), while at the same time they are willing to burn J. K. Rowling at the stake for it (Of course, I'm exaggerating again and speaking in gross over-generalizations). The point is this: it is inconsistent to dismiss Harry Potter out of hand because of its backdrop in magic and witchcraft if you are not willing to do the same with The Chronicles of Narnia and The Lord of the Rings.
Yet there are differences between Rowling on the one hand and Lewis and Tolkien on the other. Differences not so much in the use of magic or witchcraft per se, but in the underlying worldview within which the stories are framed. What is obvious in Tolkien and Lewis is that they wrote within a Christian worldview. This doesn't mean that their stories explicitly acknowledge Christianity, nor that there is always a one to one parallelism at play in their stories. Indeed, there is nothing of this in Tolkien and only bits of it in Lewis. By saying that their stories are framed by an underlying Christian worldview, I mean that the worlds they created (Narnia and Middle-Earth) correspond in moral and spiritual principles with the world created and governed by the God affirmed in the Jewish and Christian Scriptures. There is an explicit acknowledgement that the creatures of these worlds are just that - creatures, living in accountability to and under government by a higher power (again, this is more clear in Lewis than in Tolkien, but it is there in Tolkien just the same). There is a very strong and definite belief in moral absolutes - the lines between good and evil are clearly demarcated, with little if any gray in between. There is also a clear difference between the "magic" used for good and the magic used for evil, and one of the key plot threads in their stories (at least this is true for Tolkien) is the conflict faced by the protagonists when tempted to use the evil power for good purposes.
Now, it is not that these things are all entirely missing from Rowling. I want to be careful to not demonize her or her books (that has already been done enough). Some of these elements are there, but they are fainter. For example, there is definite good and definite evil (Dumbledore and Harry Potter on the one hand, and the evil Lord Voldemort, on the other), but the dividing line between good and evil is much more hazy (for example, after four novels I'm still trying to figure out just where Professor Snape fits into all of this). There are differences between the magic used for good and the magic used for evil (for example, the three "unforgivable curses" used by Lord Voldermort), although there is a fair bit of magical middle ground shared by both sides. What does seem to be missing in Harry Potter is any acknowledgement of accountability to and government by a Divine Creator. When reading The Lord of the Rings, one gets the definite sense that Frodo and Gandalf and Aragorn and the forces working for good are part of a bigger picture, being helped and guided by powers higher than themselves. This is even clearer in the Narnian stories ("Aslan is on the move"). But when reading Harry Potter you get the sense that Harry Potter's help comes either from within himself or from his dead parents - but not from any divine and good Creator-God.
Worldview questions are, I think, some of the more important things parents should consider in weighing out what their children should read. Whether the accoutrements of magic are there or not, the larger questions should be: does this story as whole portray things in its make-believe and fantasy world in true way which corresponds to things in the real world? Does good triumph over evil? Is evil met with either judgment or redemption? Do people find their help from a Source of All Powerful Goodness which is from without? Is there some kind of "providence" working out a plan behind the scenes?