Using books for "magic" is part of our real world's mythology.If we go by that thought, books are made of paper and only be used for reading, yet we use them for casting magic in PE. That is not a problem?Because lim-lim's are just fiction, but we know how books are used and how they should be treated.
Although I do find Sawyer's explanation how their wizards do so a bit heavy. I mean, a battery for a soul energy to pass through? Ehhhh...