I consider Deftones to be alternative rock with prog and post-rock influences. And Korn falls into the hard rock category for me. To be honest I'm not a big Korn fan at all, so I haven't heard most of their stuff (what I have heard I didn't like), so I could be way off base here.
Do you not consider alternative metal to be a type of music? Or if you do, what is missing about Deftones that makes them alt rock instead of alt metal? It seems odd to group them with R.E.M., U2, PJ Harvey and such.
Not a huge KoRn fan myself, though I like a few songs, but I've heard plenty from them, and I'd definitely say you're offbase. "Hard rock" has become almost a useless category with how broad it can theoretically be, but even then it's still a stretch to put KoRn in with a style more centered on AC/DC, Aerosmith and such.