It isn't more or less magic, it's what the magic means.
There is no such thing as fiction utterly divorced from reality. Everything in a fantasy book has some basis in truth. Now in Narnia, "magic" is a power posessed by essentially supernatural beings which humans aren't to mess around with. Occasionally the good supernatural beings grant it in small portions to men in order to do good, but the magic of evil beings is to be totally rejected. Now, with apologies to Lewis, who hated his works being called an "allegory," it's fairly clear that such things are after the fashion of the Christian view of the supernatural. Great powers belong to God, lesser but still great powers belong to satan. God can cause men to work miracles on occasion for his purposes, but we are to abhore satan's power.
You cannot make the same kind of comparisons with Harry Potter. These books do, however, present something much more akin to the Wiccan view. Hence, if he hasn't crossed the line into outright witchcraft, he's still playing with the line.