Remember: C.S. Lewis and J.R.R. Tolkien were the best of friends and colleagues at the time they wrote these seminal works. The similarities go back to the printed page.
Then remember that Weta Workshop and Weta Digital handled the designs for Narnia just as they did LOTR. Just as ILM and Sony have a style, so does Weta.
The similarities aren't accidental. But that doesn't mean Narnia is a rip off of LOTR either.