Hmm, maybe it's because technically Sabriel isn't the first novel in the series? Lireal was written first and is quite a bit longer so might introduce all the concepts at a better pace.
Never heard of it before. :O I haven't really picked up much YA (except in comics) in quite a while. Actually, the last YA novel I read was the first Percy Jackson, and while I really like the concept, it didn't grab me enough to continue right away. Adding The Knife of Never Letting Go to my to-read list. Thanks!